Difference in leaf and root stoichiometric characteristics of Quercus rehderiana Hand.-Mazz. in forests with rocky and non-rocky desertification in Southwest China

doi:10.21203/rs.3.rs-4932160/v1

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Difference in leaf and root stoichiometric characteristics of Quercus rehderiana Hand.-Mazz. in forests with rocky and non-rocky desertification in Southwest China

https://doi.org/10.21203/rs.3.rs-4932160/v1

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Quercus rehderiana Hand.-Mazz. is a genus of Quercus in the Fagaceae family, which widely distributed in Guizhou Province in Southwest China. It has important ecological significance in soil and water conservation, species diversity maintenance, and climate regulation. To date, the researches on stoichiometric characteristics of Quercus mainly focus on leaves, and few studies on roots. However, the difference of leaf and root stoichiometric characteristics of Quercus between in forests with rocky and non-rocky desertification are still unclear. In this study, we compared leaf (15 individuals) and root (9 individuals) carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) concentrations and their stoichiometric ratios in five 20 x 20 m quadrants of forests with rocky and non-rocky desertification. The aim was to find their resource strategies of adaptation to nutrient deficient soil environments in forests with rocky desertification. Our results show that leaf P and K concentrations in forest with non-rocky desertification were significantly higher than those in forest with rocky desertification, Ca and Mg concentrations were opposite. Root N, Ca and Mg concentrations in forest with rocky desertification were significantly higher than that in forest with non-rocky desertification, P and K concentrations were opposite. The N:P of leaves were greater than the threshold value of phosphorus (16) both in forests with rock and non-rocky desertification. Leaf P concentration was positively correlated with N concentration in forest with non-rocky desertification. Root N concentration was positively correlated with P concentration in forest with non-rocky desertification. C concentration of leaves and roots in forest with rocky desertification was negatively correlated with Ca concentration. In conclusion, leaf and root showed an obvious difference in nutrients and stoichiometric characteristics between in forests with rocky and non-rocky desertification. The growth of Q. rehderiana both in forest with rocky and non-rocky desertification was mainly limited by P. The trade-offs and synergies of nutrient absorption and utilization by different plant organs are both similar and different in different forests. Therefore, proper addition of N and P nutrients in plant growth period can promote plant growth and development, and help to improve the stability of forest ecosystem. The research results have practical significance for the vegetation restoration and protection in forests with rocky desertification.

leaf and root

nutrient limitation

Quercus rehderiana

rocky desertification forest

stoichiometric characteristics

Ecological stoichiometry is the study of the balance of energy and multiple chemical elements, providing an integrative approach to investigate the stoichiometric relationships and rules in the biogeochemical cycling and ecological processes [1, 2]. At present, the study of ecological stoichiometric characteristics of different ecosystems are mainly focus on the concentrations of carbon (C), nitrogen (N), phosphorus (P), the nutrient limitation of N and P in plants, and the indicative function of C, N and P stoichiometric characteristics on plant growth [3−7], and few studies focus on potassium (K), calcium (Ca) and magnesium (Mg) concentrations [8−10]. C is the basic element of plant tissue and participates in the synthesis of ATP and NAD(P)H [11−13]. N is the basic element of ribulose 1, 5-diphosphate carboxylase (Rubisco) [14]. P is an essential element of nucleic acids, lipid membranes, and bioenergy molecules such as ATP [15]. K is involved in the activation of various enzymes in plants, as well as in maintaining membrane potential and controlling stomatal movement [15, 16]. Ca participates in the formation of calcium pectinate, thereby stabilizing the structure of the cell wall and actively promoting the formation of cytoplasm and organelles [17]. Mg is related to photosynthesis, growth and development of plants [18]. Therefore, the study of the ecological stoichiometric characteristics of C, N, P, K, Ca and Mg in plants is of great scientific significance for understanding the coupling cycle characteristics of nutrients between plants and ecosystems, their ecological strategies and environmental adaptation mechanisms [5, 6].

The C:N:P stoichiometry of leaves and roots can reflect the survival strategies of plants in a specific environment, as well as their own growth state and internal characteristics [1, 5]. For example, C:N and C:P can reflect the growth rate of plants, and can indicate the correlation with their N and P nutrient use efficiency [4, 19, 20]. The N:P ratio indicates that plant growth is limited or not limited by N and P elements [3, 21, 22]. Specially, Koerselman et al. (1996) divided N:P into three levels: N:P > 16 (limitation of P), N:P < 14 (limitation of N), 14 < N:P < 16 (limitation of N and P or both not) [3]. In addition, N:K and K:P ratios are indicators for K or K + N limitation of plant growth, that is, N:K < 2.1 and K:P > 3.4 indicate that K or K + N limitation of plant growth [8]. Previous studies reported that the growth of terrestrial plants in China is mainly limited by soil P [23], especially in tropical rainforests [24] and desert ecosystems [25], while it is mainly limited by N in high-altitude subtropical forest ecosystems [26, 27]. Interestingly, the growth of karst rocky desertification plants may be limited by N or P, or both N and P [28−30].

The karst rocky desertification is a typical ecological fragile region with high rock exposure rate, thin soil layer, poor soil nutrient, and high calcium carbonate concentration [31, 32]. To date, although many studies have focused on nutrients concentration and ecological stoichiometry of leaves, roots and their relationships [20,33−35], while the differences between in forests with rocky and non-rocky desertification are rarely reported [36]. Q. rehderiana is one of the species of Quercus Sect. Heterobalanus plants in Fagaceae family, which have important ecological significance and economic value (in terms of biodiversity maintenance, soil and water conservation, carbon storage etc.), which widely distributed in Guizhou Province both in forests with rocky desertification and non-rocky desertification [37]. To date, few studies focus on leaf stoichiometric characteristics of Quercus [38−41]. For example, the growth of Q. semicarpifolia in Subalpine zone of Hengduan Mountains is not limited by N and P [40]. Li et al. (2018) reported that the growth of Quercus sect Heterobalanus in Hengduan Mountain Region is limited by N [39]. Liu et al. (2012) reported that the growth of Quercus aquifolioides in Sichuan Province is limited by N [38]. However, studied in karst rocky desertification region in Guizhou Province found that the growth of 2 species of Quercus is limited by P [41]. Therefore, more evidence is needed on whether Quercus growth is limited by N or P.

Due to forests with rocky desertification are widely deficient in nutrients (more P limitation), resulting in lower potassium and phosphorus concentrations in plants. However, leaf nutrient acquisition is dependent on root absorption and transportation. Therefore, we hypothesized that Q. rehderiana leaves and roots in forests with rocky desertification have higher N:P ratio but lower potassium and phosphorus concentrations than in forest with non-rocky desertification. In addition, forests with rocky desertification are rich in magnesium and calcium, resulting in enrichment of magnesium and calcium in plants. Therefore, we hypothesized that Q. rehderiana leaves and roots in forests with rocky desertification have higher magnesium and calcium concentrations than in forest with non-rocky desertification. The results of this study can provide practical significance for biodiversity conservation and restoration of rocky desertification.

2.1 Study area

The study area was located in Weining, Bijie City, Guizhou Province, southwest China (103º36'−104º30' E, 26º30'−27º25' N; 2200 m a.s.l.). The research site is influenced by the subtropical monsoon climate. The mean annual temperature is 12 ºC and the mean annual precipitation is ca. 1000 mm. The soil types include purple soil, yellow brown soil and yellow soil, the pH value is 5.50. The study area is frequently disturbed by natural or man-made disturbances, such as logging and grazing. The shrub layer is dominant by Coriaria nepalensis, Rhododendron simsii, and Corylus yunnanensis. The herbaceous layer is dominant by Arthraxon hispida, Plantago asiatica, and Rubia cordifolia [42].

2.2 Sampling

According to classification of rocky desertification (vegetation coverage < 50%, rock exposure > 60%, average soil thickness < 15 cm) and non-rocky desertification (vegetation coverage > 50%, rock exposure < 60%, average soil thickness > 15 cm) [43], we set five quadrates (20 m × 20 m) in forests with rocky desertification (top of the mountain) and non-rocky desertification (foot of the mountain), respectively. For each 20 m × 20 m quadrat, we divided into four small quadrats of 10 m × 10 m. Three small quadrats were selected as sample sampling quadrats for leaves and roots due to some small quadrats in the forests with rocky desertification was no Q. rehderiana. We used high pruning to cut branches of Q. rehderiana near the center of each small quadrat, and then collected healthy, mature, sun-exposed and intact leaves. After leaf samples were collected, two individuals of Q. rehderiana on the diagonal of 20 m × 20 m quadrate were selected to dig roots. We selected roots with diameters less than 2 mm as samples. The experimental material complies with institutional, national, and international guidelines and legislation. The plant samples collected were approved by the Weining County Forestry Bureau, Bijie City, Guizhou Province. The specimen (specimen number: SC-a-054-B01) was authenticated by Research assistant Hu Jun of Chengdu Institute of Biology, Chinese Academy of Sciences and stored in the Herbarium of Chengdu Institute of Biology, Chinese Academy of Sciences. In order to protect the monitoring plots from serious damage, two individuals were selected to dig root samples for each 20 m × 20 m quadrate. In the forest with rocky desertification, in total of 9 root samples were collected because many stones could not be dug. We put the leaf and root samples into a sampling box, add some ice packs and brought it back to the laboratory. Leaf and root samples are washed with tap water to remove dirt and sand, and then washed with distilled water for 3 times. Leaf and root samples were oven-dried at 70°C for 48 h and 72 h, respectively. We use a crusher to crush dried leaf and root samples and pass them through a 60-mesh sieve.

2.3 Sample determination

We used a Dumas-type combustion C-N elemental analyzer (Vario MAX CN, Elementar Analysensysteme GmbH, Hanau, Germany) to determine nitrogen concentration (N) and carbon concentration (C) in leaves and roots. We used an inductively coupled plasma atomic-emission spectrometer (iCAP 7400, Thermo Fisher Scientific, Bremen, Germany) to determine phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) in leaves and roots [22, 24]. The stoichiometric ratio of C, N, P, K, Ca and Mg were calculated based on nutrient concentrations.

2.4 Data analyses

Data on the leaf and root nutrients and their stoichiometric ratio were used for single individuals. The difference of leaf and root nutrients, stoichiometric ratio between in forests with rocky and non-rocky desertification was analyzed with an independent sample t-test, using the stats package. The correlation between nutrients of leaf and root was analyzed with Pearson’s correlation, using the Hmisc package. A principal component analysis (PCA) was performed to evaluate trait associations, using the vegan package. Data were log₁₀-transformed to improve the normality of distribution before Pearson’s and PCA analysis. All analyses were used in R version 4.4.0 (R Core Team 2024).

3.1 Difference of leaf and root nutrients

The P and K of leaves in the forests with non-rocky desertification were significantly higher than those in the forests with rocky desertification (Fig. 1C,D). The Ca and Mg of leaves in the forests with rocky desertification were significantly higher than those in forests with non-rocky desertification (Fig. 1E,F). There were no significant differences in leaf C and N between forests with rocky and non-rocky desertification (Fig. 1A,B). The N of roots in the forests with rocky desertification were significantly higher than those in the forests with non-rocky desertification (Fig. 1B). The P and K of roots in the forests with non-rocky desertification were significantly higher than those in the forests with rocky desertification (Fig. 1C,D). The Ca and Mg of roots in the forests with rocky desertification were significantly higher than those in forests with non-rocky desertification (Fig. 1E,F).

3.2 Difference of leaf and root stoichiometric characteristics

The C:P, N:P and N:K ratios of leaves in the forests with non-rocky desertification forest was significantly higher than those in forest with rocky desertification (Fig. 2B,C,D; Table 1). The K:P ratio of leaves in the forests with rocky desertification forest was significantly higher than those in forest with non-rocky desertification (Fig. 2E). There were no significant differences in leaf C:N ratio between forests with rocky and non-rocky desertification (Fig. 2A). The C:N ratio of roots in the forests with non-rocky desertification forest was significantly higher than those in forest with rocky desertification (Fig. 2A; Table 1). The C:P, N:P and N:K ratios of roots in the forests with rocky desertification forest was significantly higher than those in forest with non-rocky desertification (Fig. 2B,C,D). There were no significant differences in root K:P ratio between forests with rocky and non-rocky desertification (Fig. 2E).

Table 1

Leaf and root stoichiometric characteristics of *Quercus rehderiana* Hand.-Mazz. in forests with rocky and non-rocky desertification (mean ± standard error).
Stoichiometric characteristics	Forests with rocky desertification		Forests with non-rocky desertification
Stoichiometric characteristics	Leaf	Root	Leaf	Root
C	498.00±1.54	466.65±1.75	494.80±1.31	469.70±2.89
N	15.01±0.19	4.56±0.16	15.34±0.31	3.73±0.20
P	0.82±0.02	0.33±0.01	0.97±0.03	0.51±0.02
K	3.67±0.22	1.37±0.08	6.15±0.20	2.34±0.36
Ca	9.29±0.85	21.51±1.22	6.61±0.47	7.53±0.62
Mg	1.33±0.09	0.75±0.04	1.05±0.07	0.50±0.06
C:N	33.25±0.41	103.42±3.19	32.44±0.64	129.66±8.06
C:P	612.62±16.92	1440.39±55.78	520.61±17.16	946.38±47.67
N:P	18.47±0.57	13.94±0.38	16.04±0.41	7.61±0.66
N:K	4.33±0.29	3.36±0.12	2.53±0.09	1.94±0.28
K:P	4.51±0.25	4.19±0.19	6.48±0.31	4.66±0.66

3.3 Bivariate relationships of leaf and root stoichiometric characteristics

For leaf nutrients, P was positively related to N in forests with non-rocky desertification (R = 0.63, p = 0.012), but this relationship was not significant in forests with rocky desertification (R = − 0.01, p = 0.99) (Fig. 3A). C was negatively related to Ca in forests with rocky desertification forest (R = − 0.79, p < 0.001), but this relationship was not significant in forests with non-rocky desertification (R = − 0.23, p = 0.400) (Fig. 3B). For root nutrients, P was positively related to N in forests with rocky desertification (R = 0.77, p = 0.015), but this relationship was not significant in forests with non-rocky desertification (R = − 0.52, p = 0.150) (Fig. 3C). C was negatively related with Ca (R = − 0.86, p = 0.003) and Mg (R = − 0.85, p = 0.004) in forests with non-rocky desertification forest, but this relationship was not significant in forests with rocky desertification (R = − 0.03, p = 0.940; R = − 0.30, p = 0.40) (Fig. 3D,E).

3.4 Association between leaf and root stoichiometric characteristics

The results of the PCA showed that the first and second components accounted for 67.48% and 20.22% of the total variance, respectively (Fig. 4). The first axis was positively correlated with Ca, C:P, and C:N. At the opposite end were N, P, and K. The second axis correlated positively with Ca, Mg, N:P, and N:K, negatively with K:P. Leaf in forests with non-rocky desertification exhibited a positive correlation with high N, N:P, N:K, and Mg. Leaf in forests with rocky desertification exhibited a positive correlation with high P, K, and P:K. Root in forests with non-rocky desertification exhibited a positive correlation with high C:N. Root in forests with rocky desertification exhibited a positive correlation with high Ca and C:P. Leaf and root nutrients with rocky desertification and non-rocky desertification overlapped less in the multivariate trait space, indicating that the nutrient strategies were different (Fig. 4).

Our results showed that Q. rehderiana leaves and roots in forests with rocky desertification have higher N:P ratio but lower K and P concentrations than in forests with non-rocky desertification, which was consistent with our first hypothesis (Figs. 1 and 2). In addition, we find that Q. rehderiana leaves and roots in forests with rocky desertification have higher Mg and Ca concentrations than in forests with non-rocky desertification, which was consistent with our second hypothesis (Figs. 1 and 2).

Compared with other studies, the results of this study demonstrate that C concentration of Q. rehderiana leaves both in forests with rocky desertification (498.0 mg g⁻¹) and non-rocky desertification (494.8 mg g⁻¹) had higher than those of global terrestrial plant species (464.0 mg g⁻¹) [44], 10 species in the Maolan forests with karst rocky desertification (386.6 mg g⁻¹) [36], 10 dominant species in Guiyang forests with karst rocky desertification (438.96 mg g⁻¹) [29], but similar to the study of Guangxi forests with karst rocky desertification (496.1 mg g⁻¹) and Quercus Sect. Heterobalanus shrubs in the Henduan Mountain region (477.9 mg g⁻¹) [37], indicating that Q. rehderiana have higher C storage capacity both in forests with rocky desertification and non-rocky desertification. Leaf N and P concentrations of Q. rehderiana in forests with rocky desertification (15.01 mg g⁻¹, 0.82 mg g⁻¹) and non-rocky desertification (15.34 mg g⁻¹, 0.97 mg g⁻¹) had lower than those reported by Han et al. (2005) [23] and Ren et al. (2007) [45] for large-scale plant species in China (19.7 mg g⁻¹, 1.5 mg g⁻¹), indicating that the distribution region of Quercus Sect. Heterobalanus was deficiency in nitrogen. Similar result has been reported by Li et al. (2018) in Hengduan Mountain region [39]. Leaf P concentration of Q. rehderiana in forests with non-rocky desertification had higher than those in forest with rocky desertification. This may be due to the high rock exposure rate, severe wind erosion, and heavy rainfall in the study area greatly weakened the retention of N and P in soil, resulting in poor soil N and P [46−48]. Therefore, the concentrations of N and P of Q. rehderiana leaves were relatively low. We find that leaf Ca and Mg concentrations of Q. rehderiana in forests with rocky desertification was significantly higher than those in forests with non-rocky desertification, and the leaf K concentration was significantly lower than those in forest with rocky desertification. The results are consistent with the comparative study of leaf nutrient concentrations between in forests with rocky desertification and non-rocky desertification in Guangxi and Guizhou Provence [49]. Compared with other studies, the results of our study showed that leaf K concentration of Q. rehderiana both in forests with rocky desertification (3.67 mg g⁻¹) and non-rocky desertification (6.15 mg g⁻¹) were significantly lower than those of Maolan forests with karst rocky desertification (11.58 mg g⁻¹) [20] and Guiyang forests with karst rocky desertification (12.25 mg g⁻¹) [50]. This may be that plants selectively absorb and enrich more K to improve their resistance to adapt to the harsh habitat, shallow soil layer, and poor water and nutrient conservation ability in forests karst rocky desertification [50, 51]. K concentration of Q. rehderiana leaves in our study was lower than those in other forests with rocky desertification, which may be due to the degree of rocky desertification in this study was lower than other forests. Ca concentration of Q. rehderiana leaves in forests with rocky desertification (9.29 mg g⁻¹) had higher than the average Ca concentration of terrestrial plant species in China (8.81 mg g⁻¹) [23], opposite in forests with non-rocky desertification (6.61 mg g⁻¹). Mg concentration of Q. rehderiana leaves both in forests with rocky desertification (1.33 mg g⁻¹) and non-rocky desertification (1.05 mg g⁻¹) were significantly lower than Maolan forests with karst rocky desertification (5.29 mg g⁻¹) [28], but significantly higher than that Liu et al. (2024) reported (0.33 mg g⁻¹) [49]. Ca and Mg concentrations of Q. rehderiana leaves in forests with rocky desertification were significantly higher than those in forests with non-rocky desertification. The chemical dissolution of soluble carbonate rocks by ground water and surface water in karst rocky desertification area makes calcium and magnesium enrichment in soil and then accumulation in plants [52].

The roots absorb water, minerals and nutrients and transport them to the leaves, ensuring the normal metabolism of the leaves [53]. In the present study, we find that roots N, Ca and Mg concentrations of Q. rehderiana had significant greater in forests with rocky desertification than those in forests with difference between in forests with non-rocky desertification, P and K concentrations showed opposite. Compared with other studies, C concentration of roots of Q. rehderiana both in forests with rocky desertification (466.7 mg g⁻¹) and non-rocky desertification (469.7 mg g⁻¹) was similar to terrestrial plant roots of China (473.9 mg g⁻¹) [54], but higher than those in Quercus Sect. Heterobalanus shrubs in the Henduan Mountain region (431.4 mg g⁻¹) [39] and Guanling forests with karst rocky desertification in Guizhou Province (445.6 mg g⁻¹) [30], indicating that Q. rehderiana roots have higher C storage capacity. N concentration of Q. rehderiana roots both in forests with rocky desertification (4.56 mg g⁻¹) and non-rocky desertification (3.73 mg g⁻¹) had lower than terrestrial plant roots in China (9.16 mg g⁻¹) [54] and Guanling forest with karst rocky desertification in Guizhou Province (5.98 mg g⁻¹) [30]. P concentration of Q. rehderiana roots in forests with non-rocky desertification (0.97 mg g⁻¹) was similar to terrestrial plant roots in China (0.95 mg g⁻¹) [54] and Guanling forests with karst rocky desertification in Guizhou Provence (0.95 mg g⁻¹) [30], but lower in forests with rocky desertification (0.82 mg g⁻¹). On the one hand, plants growing in forests with rocky desertification had lower ability to acquire N and P from soil than plants growing in forests with non-rocky desertification [33]. On the other hand, the high rock exposure rate, severe wind erosion, and heavy rainfall in the study area greatly weakened the soil retention of N and P elements, resulting in relatively poor soil N and P [46, 55]. K concentration of Q. rehderiana roots both in forests with rocky desertification (1.37 mg g⁻¹) and non-rocky desertification (2.34 mg g⁻¹) had lower than those observed in Guanling forests with karst rocky desertification (2.71 mg g⁻¹) [30], and in Hunan forests with non-rocky desertification (2.57 mg g⁻¹) [56]. Moreover, we find that K concentration of roots in forests with rocky desertification was significantly higher than those of non-rocky desertification. Karst rocky desertification areas are poor-soil and soil erosion serious, therefore plant roots and leaves will selectively absorb and enrich more K element to increase the resistance to the severe environment [51]. Similar to leaves, Ca and Mg concentrations of roots in forests with rocky desertification was significantly higher than those in forests with non-rocky desertification. It may be due to soils are enrichment in Ca and Mg in forests with rocky desertification, which are absorbed by the roots and enriched them in plant roots [52].

The C, N, and P stoichiometry of plants can indicate the C accumulation dynamics, growth rate, and N and P nutrient limitation patterns of the terrestrial ecosystem [57, 58]. To a certain extent, C:N and C:P ratios of mature leaves reflect the growth rate of plants, that is, plants with higher C:N and C:P ratios have higher N and P utilization efficiency but low growth rate [59]. In this study, C:N and C:P ratios of Q. rehderiana leaves in forests with rocky desertification (33.25, 612.6) and non-rocky desertification (32.44, 520.6) were significantly higher than the global terrestrial plant (30.9, 374.7) [44]. The results are consistent with those of the Quercus Sect. Heterobalanus shrubs in Hengduan Mountain area [39] and other Quercus in karst peak-cluster depression in Guizhou Provence [41]. In this study, both C:N and C:P ratios were higher in forests with rocky and non-rocky desertification, indicating higher N and P utilization efficiency, but lower growth rate. This may be one of the important reasons for the wide distribution of Q. rehderiana in rocky desertification and non-rocky desertification environment [41]. The N:P ratio as an indicator of nutrient limitation, which divided into three level: N:P > 16 (P limitation), N:P < 14 (N limitation), 14 < N:P < 16 (limitation of N and P or both not) [3]. In this study, N:P ratio was higher than 16 both in forests with rocky desertification (18.47) and non-rocky desertification (16.04), indicating that the growth of Q. rehderiana was mainly limited by P. Interestingly, studies of Quercus in the Hengduan Mountain area found that the growth of Quercus Sect. Heterobalanus shrubs were mainly limited by N [39], while Quercus semicarpifolia was not limited by N and P [40]. The N:K and K:P ratios are indicators that plant growth was limited by K or N + K, N:K < 2.1 and K:P < 3.4 indicate that plant growth was limited by K or N + K, and the opposite was not limited [8]. We find that N:K and P:K ratios both in forests with rocky desertification (4.33, 4.51) and non-rocky desertification (2.53, 6.48) were higher than 2.1 and 3.4, respectively. Therefore, the growth and development of Q. rehderiana both in forests with rocky desertification and non-rocky desertification was not limited by K, which consistent with reported by Liu et al. (2024) [49].

The C:N and C:P ratios of roots reflects the turnover ability of root, that is, the higher the C:N ratio which have slower turnover rate of root [60, 61]. Our study found that C:N ratio of Q. rehderiana roots in forests with rocky desertification (103.42) and non-rocky desertification (129.66) were significantly higher than the average value of terrestrial vegetation ecosystem in China (59.15) [54], in forest with karst rocky desertification (59.15) [30], and in forests with non-rocky desertification (105.33) [39]. Compared with other species of Quercus, C:N ratio of Q. rehderiana roots in forests with rocky desertification and non-rocky desertification were higher than those of other Quercus species in forests with karst rocky desertification, such as Quercus fabrei (75.67) and Quercus fabrei (77.36) [41]. We also found that C:P ratio of Q. rehderiana roots in forests with rocky desertification (1440.39) and non-rocky desertification (946.38) were significantly higher than the average value of terrestrial vegetation in China (844.07) [54], in forests with karst rocky desertification (962.06) [30], and Quercus Sect. Heterobalanus shrubs in forests with non-rocky desertification (418.15) [39], but similar to Quercus fabrei (1398.99) and Quercus fabrei (1233.43) studied in forests with karst rocky desertification [41]. Therefore, we concluded that the slow decomposition rate of roots of Q. rehderiana may be related to soil microorganisms, Quercus species heterogeneity and karst rocky desertification environment. Based on previous studies, Chen et al. (2011) suggested that the N:P threshold of 12 and 14 is also applicable to plant tissues such as roots, which divided into N:P < 12 (limitation of N), N:P > 14 (limitation of P) and 12 < N:P < 14 (limitation of N and P) [9]. In this study, root N:P ratio in forests with rocky desertification was 13.94, indicating that the root growth of Q. rehderiana was limited by both N and P. However, root N:P ratio in forests with non-rocky desertification was 7.61, indicating that the root growth of Q. rehderiana was limited by N. The results of this study are similar to those of the regional studies, that is, the N:P ratio of the roots in forests with karst non-rocky desertification were limited by N, while leaves were limited by P [36]. The N:P ratio of plants is limited by P probably may be due to the availability of active N is greater than P [21].

The distribution of nutrients in different organs varies greatly due to the function and activity of different organs of the plant, and organs that are metabolically active (leaf photosynthesis and root absorption capacity) tend to allocate more nutrients (such as N, P, K, Ca, etc.) to maintain higher function [62, 63]. The order of C, N, and P concentrations were consistent in different plant components from the forests with rocky desertification and non-rocky desertification, specifically, leaves > roots. Our study results are consistent with the research of 930 species plants in eastern of China [62], the research of 10 dominant tree species in the central of Guizhou karst region [29], the research of 3 species for Quercus in karst peak-cluster depressions in southern of Guizhou [41], the research of 6 species for Quercus Sect. Heterobalanus shrubs in the Hengduan Mountain, China [39], and research of 10 tree species in the Guizhou plateau karst secondary forest [34]. This indicates that nutrient distribution strategies in plant organs are related to the function of plant organs at regional scale, ecosystem scale and for plant individual. The order of Ca, K and Mg concentrations in our study were the consistent in different plant components from the rocky desertification forest and non-rocky desertification forest, specifically, leaves > roots. In order to ensure the growth and development of plants, plants distribute more nutrients to leaves to photosynthesis, while roots, as an absorption and transportation organ and store less nutrients [64].

For the correlation of nutrients, leaf N and P concentrations were significantly positively correlated in forests with non-rocky desertification, which was similar to the results of other studies [23, 36, 39]. This is because plants need to consume a large amount of ATP to synthesize proteins during the growth process, which reflects the synergism of plant absorption of N and P [65]. Leaf P concentration was positively related to leaf Mg concentration in forests with non-rocky desertification, which was consistent with previous studies [28, 49]. The results showed that there is a certain proportion composition and coordination relationships between these elements [28, 66]. Leaf Ca concentration was negatively related to leaf C concentration in forests with rocky desertification, which was consistent with previous studies in forests with karts rocky desertification in Yunnan Provence [67] and in Guizhou Provence [68]. Interestingly, C and Ca concentrations correlations in roots are similar to those in leaves, suggesting that the same synergistic tradeoff relationship between roots and leaves. Under the stress of high Ca environment, the chlorophyll content, stomatal conductance, transpiration rate, and the photosynthetic production of plants were reduced, which was not conducive to C storage [68–70]. We find that root C concentration in forests with rocky desertification was negatively correlated with Mg concentration, which consistent with other study in forests with karst rocky desertification [68]. The Mg concentration in leaves and roots in forests with rocky desertification are generally high, which can inhibit the phosphorylation process of photosynthesis, thereby reducing plant productivity and thus affecting carbon storage in leaves and roots [71].

In conclusion, we compared the stoichiometric characteristics of Q. rehderiana leaves and roots in forests with rocky and non-rocky desertification. We found that leaf and root nutrient traits and stoichiometric characteristics have significance difference between forests with rocky and non-rocky desertification. Forests with rocky desertification had higher leaf and root Ca and Mg concentrations, and N:P ratio, while forests with non-rocky desertification had higher leaf and root P and K concentrations. Leaf and roots in forests with rocky and non-rocky desertification adopted different nutrient resource strategies. The growth of Q. rehderiana in forests with rocky and non-rocky desertification were limited by P. Therefore, we suggested that proper addition of N and P nutrients in plant growth stage can promote plant growth and development, and enhance the stability of forest ecosystem.

Ethics approval and consent to participate

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Competing interests

The authors declare no competing interests.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Data access link: https://orcid.org/0000-0002-3782-8165. All data generated during the current study are included in this published article.

Funding

This study was financially supported by the Bijie Science and Technology Project (bikelianhe[2023]23), the Bijie Science and Technology Project (bikelianhe[2023]10), the Project of Guizhou Science and Technology Fund(qiankehejichu-ZK-[2024]key077)，the Guizhou Provincial Science and Technology Project (qiankehejichu-ZK-[2022]yiban167), the Bijie Talent Team of Biological Protection and Ecological Restoration in Liuchong River Basin (202112), and the Regional First-Class Discipline of Ecology in Guizhou Province (XKTJ[2020]22).

Acknowledgments

The author thank to the Public Technology Service Center of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences for analyzing the leaf and root nutrient concentrations. The Weining County Forestry Bureau provided logistic support.

Author contributions

XLB and WJL conceived and designed the research. XBL, TF, SZ and YC contributed to the investigation. XLB and BH analyzed data. XLB and WJL wrote the original draft. All authors read and approved the manuscript. All authors agree to be accountable for the final manuscript. The authors read and approved the final manuscript.

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Difference in leaf and root stoichiometric characteristics of Quercus rehderiana Hand.-Mazz. in forests with rocky and non-rocky desertification in Southwest China

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Abstract

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1. Introduction

2. Materials and Methods

2.1 Study area

2.2 Sampling

2.3 Sample determination

2.4 Data analyses

3. Results

3.1 Difference of leaf and root nutrients

3.2 Difference of leaf and root stoichiometric characteristics

3.3 Bivariate relationships of leaf and root stoichiometric characteristics

3.4 Association between leaf and root stoichiometric characteristics

4. Discussion

5. Conclusions

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