-->Special Subject： Karst plants

Research progress on carbon cycle of karst vegetation in Southwest China

2022/7/20 10:21:33

Because the karst critical zone is an important part of the Earth Critical Zone system, the vegetation in karst area is an important carbon sink of terrestrial ecosystem, and the aboveground part of the vegetation in the karst area sequestrates carbon through plant growth, the carbon storage in the underground part is also very considerable, the growth of underground biomass and decomposition of litter also increase soil organic carbon and inorganic carbon content. Therefore, vegetation carbon cycle in karst area is one of the hotspots of karst carbon sink research. Based on the reviewing of research literature on carbon sequestration of karst vegetation in the past 40 years, this paper expounds the unique physiological characteristics of karst vegetation in Southwest China, and focuses on the following four aspects:(1)Evaluation of vegetation biomass, productivity and carbon storage in karst area of Southwest China;(2)Temporal and spatial variation patterns of vegetation and carbon source and sink effect in karst area of Southwest China;(3)Special mechanism of vegetation carbon utilization in karst area;(4)Prediction of vegetation carbon cycle model and carbon sink potential in karst area. The problems existing in the current research are put forward, and the future research direction is prospected. It is proposed that the future research should be carried out in the aspects of systematic determination of relevant parameters and mechanism process of vegetation carbon cycle in karst area, fine identification of vegetation landscape types in southwest karst area, quantification of carbon sequestration process, and correction and modification of karst vegetation carbon cycle model. This paper provides a reference for in-depth understanding the temporal and spatial evolution of carbon cycle in karst region and for exploring regional carbon cycle mechanism.

Estimation of plant leaf chlorophyll content based on spectral index in karst areas

2022/7/20 10:21:33

Leaf chlorophyll content is central to carbon, water and energy exchange between the biosphere and the atmosphere, also to the terrestrial ecosystem function. Quantitative estimates of leaf chlorophyll content with hyperspectral imagery can provide scientific insight for assessing plant's growth and stress as affected by abiotic and biotic factors. However, few studies have been conducted on the application of spectral indexes in estimation of leaf chlorophyll contents of plants in karst areas, especially in South China. After a review of the application of common spectral indexes in estimation of leaf biochemistry parameters, we found that most of the common spectral indexes were developed based on the difference, simple ratios, normalized difference and inverse difference formulation of leaf spectral reflectance. Therefore, we firstly measured the raw reflectance spectra of leaves from four typical karst species, namely Vitex negundo, Rhus chinensis, Celtis sinensis and Alchornea trewioides with a ASD Field Spec 4(Analytical Spectral Devices, Inc., Boulder, Colorado, US)spectrometers. We then used the above-mentioned four formulations to process the raw reflectance spectra and their first-order derivative spectra. Finally, we analyzed the relation between leaf chlorophyll contents and relative leaf raw reflectance spectra and their first-order derivative spectra, and tried to propose the best spectral index for estimation leaf chlorophyll content of plants of karst areas in South China. The results were as follows:(1)Among the common spectral indexes, the modified normalized difference vegetation index(mND705)performed well in estimation leaf chlorophyll contents of four typical karst species in term of the determination coefficient(R2 was equal to 0.45)and root mean squared error(RMSE was equal to 0.26 mg·g^-1).(2)However, most of the common spectral indices were not suitable for estimation leaf chlorophyll content of plants in karst areas. Thought the prediction capability of fluorescence ratio index(FRI1)and chlorophyll absorption area index(CAAI)were almost the same in estimation of leaf chlorophyll content of plants in karst and non-karst areas, their accuracy of prediction was relative low according to the determination coefficient.(3)The spectral indices proposed in this study performed well in estimation leaf chlorophyll content of plants in karst areas either based on the raw reflectance spectra or their first-order derivative spectra compared against others common spectral indexes, especially for the difference spectral index based on the first-order derivative spectra [dD(760, 769)]. Its determination coefficient was 0.71 and the root mean squared error was 0.19 mg·g^-1. We, therefore proposed that the difference spectral index based on the first-order derivative spectra [dD(760, 769)] can be used for estimation leaf chlorophyll content of plants in karst areas. Our results indicated that leaf chlorophyll content of plants in karst areas can be quickly and quantitatively estimated using spectral index combined with hyperspectral remote sensing data. These results can also provide scientific insights for estimating plants' growth and their adaptation to environmental stress.

Effects of soil nutrients on functional traits of Juglans sigillata in karst rocky desertification areas

2022/7/20 10:21:33

To explore the characteristics and influencing factors of leaf functional traits of plants in karst rocky desertification areas, and to reveal their adaptation mechanism to rocky desertification environment, this study reveals the effects of soil nutrients on leaf structure and photosynthetic traits in Juglans sigillata from the karstic plateau canyon areas of South China. The results were as follows:(1)The functional traits of blister J. sigillata leaves decreased with increasing rocky desertification grade, leaf area decreased, specific leaf area increased, leaf dry matter content and leaf tissue density decreased first and then increased, transpiration rate, intercellular CO₂ concentration, stomatal conductance and light energy utilization decreased and then increased, and the trends of other traits were not significant.(2)Redundancy analysis(RDA)showed that soil nutrients explained 37.4% of the variation in photosynthetic traits and 53.4% of the variation in structural traits, with total phosphorus and dissolved organic carbon having the greatest influence on photosynthetic traits, while the most significant effects on structural traits were alkali hydrolyzed nitrogen and available phosphorus.(3)Specific leaf area was highly significantly negatively correlated with leaf dry matter content and highly significantly positively correlated with net photosynthetic rate, leaf thickness was highly significantly negatively correlated with leaf tissue density, transpiration rate was highly significantly positively correlated with intercellular CO₂ concentration and stomatal conductance, water use efficiency was highly significantly negatively correlated with transpiration rate, intercellular CO₂ concentration and stomatal conductance, respectively, light energy utilization was significantly positively correlated with net photosynthetic rate. The results suggest that blister J. sigillata adapts to the special habitat of karstic desertification through a pioneering growth strategy of enhancing growth functional traits while improving resource acquisition capacity to improve resistance and adaptation to environmental stresses.

Characteristics of soil microbial community structure of three plantations in a karst region

2022/7/20 10:21:33

In order to reveal the effects of different vegetation restoration modes on soil microbial communities in karst areas, this study took pure Dalbergia odorifera plantation(PDOP), pure Acrocarpus fraxinifolius plantation(PAFP)and their mixed plantation(MADP)as research subjects. The soil microbial biomass and microbial community structure of different plantations were analyzed by chloroform fumigation extraction method and phospholipid fatty acid(PLFA)method. The results were as follows:(1)The soil microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)contents of PDOP were significantly higher than those of PAFP and MADP, and that of PAFP was significantly higher than that of the MADP.(2)The contents of soil fungi, arbuscular mycorrhizal fungi(AMF)and total PLFA were not significantly different among the three plantations, but the contents of soil bacteria, actinomycetes, AMF and total PLFA in PDOP were higher than those in PAFP and MADP, and those in the PAFP were higher than those in MADP. The PLFA contents of bacteria, gram-positive bacteria, gram-negative bacteria and actinomycetes in PDOP were significantly higher than those in MADP. The ratio of fungi to bacteria in MADP was significantly higher than that in PDOP, but there were no significant differences between MADP and PAFP.(3)Redundancy analysis showed that soil cation exchange capacity, pH, and C:N were the most important factors affecting the functional group composition of soil microbial community. From the perspective of soil microbial biomass and microbial community structure of the three plantations, MADP in karst area don't show the advantage of mixed forest in acid soil region to improve soil microbial community structure. However, the ratio of fungi to bacteria in the mixed plantation is the highest, which is more conducive to improving the stability of soil ecosystem.

Seed germination characteristics of Keteleeria calcarea, a precious tree species in karst area

2022/7/20 10:21:33

Keteleeria calcarea is a precious tree species in the mid-subtropical karst area, this species has a narrow distribution range and very few seedlings in wild populations, which severely limits the natural renewal of the population. In order to explore the causes for the endangerment of this species and provide reference for its protection and utilization, the cones and seeds morphological characteristics of K. calcarea were measured, and the effects of temperatures, light conditions, soil water contents, substrates, storage temperatures and time, and different geographical provenances on seed germination were studied. The results were as follows:(1)The average seed setting rate of K. calcarea cone was 7.45%±6.54%, the seed wing length was(2.27±0.32)cm, the average seed length was(1.55±0.15)cm(excluding seed wing), the average width was(0.62±0.05)cm, the average thickness was(0.46±0.04)cm, and the average 1 000-seed weight was(214.81±14.76)g, the average water content of dried seeds was 15.28%±1.66%.(2)The optimum temperature for seed germination was 25 ℃, and the germination rate decreased significantly at 20 ℃ and 30 ℃(P<0.05); Seed germination did not need light, but the germination rate under periodic light was significantly higher than that under continuous light and continuous darkness(P<0.05); The seeds could germinate under the conditions of 10%-30% soil water contents, and could withstand a certain degree of drought; Peat soil and perlite with loose texture and good air permeability were suitable for germination; The seeds were not resistant to storage and should be sown in time after collection; The seed germination rate of Sanjiang population in Gongcheng County of Guilin was the highest among the three geographical provenances. The seed setting rate of K. calcarea cone was low, the seed germination was strict with temperature, and the seed was easy to lose vigor, which may be an important reason for its endangerment.

Carbon and nitrogen stable isotopes of vegetation succession stages in karst plateau gorge area of Beipanjiang in southwestern Guizhou

2022/7/20 10:21:33

To explore the variations and internal relations between the carbon and nitrogen(C and N), and the carbon and nitrogen stable isotope(δ¹³C and δ¹⁵N)with succession proceeding. Four succession stages about forest communities in karst plateau gorge area were selected as the subjects, which were herbage-shrub, shrub, tree-shrub and tree. By measuring C, N and stable isotope ratios in leaf-litter-soil to analyze their interaction effects among different levels. The results were as follows:(1)The δ¹³C values of leaf-litter-soil in karst forest were -31.31‰--28.23‰, -29.96‰--20.07‰, -26.83‰--21.14‰ respectively, and the corresponding δ¹⁵N values were -3.41‰-1.54‰, -2.61‰-0.99‰ and 5.36‰-8.63‰, generally, the soil showed a more enrichment effect.(2)With the succession, the leaf δ¹³C and soil δ¹⁵N values increased first and then decreased, while the soil and litter δ¹³C values decreased, and there were no obvious changing rules about the leaf and litter δ¹⁵N values.(3)The leaf-soil δ¹⁵N values at the tree-shrub stage was the lowest, indicating the stage with low N saturation and relatively deficient N content.(4)The correlations among the leaf-soil C, N and their isotopes were strong, demonstrating that the both cycles were closely relevant with the significant inhibiting or promoting effects. In conclusion, in order to improve the self-regulation ability of the ecosystem to resource utilization and nutrient absorption, the tree species with high water use efficiency, such as Lindera pulcherima, Triadica rotundifolia and Cladrastis platycarpa, should be applied for ecosystem restoration in this area.

Effects of different land use and ecological restoration types on soil enzymatic C:N:P ratios in a karst ecosystem

2022/7/20 10:21:33

To explore the effects of land use and ecological restoration types on soil enzyme activities and C:N:P ratios in the karst ecosystem, we selected three land use types [disturbed land, pasture grassland, and orchard forest(loquat)] and four restoration types(evergreen forest, deciduous forest, evergreen-deciduous mixed forest, and natural restoration forest), which are long-term positioning observation experimental plots of the Huanjiang Observation and Research Station for Karst Ecosystems, measured the activities of four soil enzymes [β-1,4-glucosidase(βG), β-1,4-N-acetylglucosaminidase(NAG), leucine aminopeptidase(LAP), and alkaline phosphatase(ALP)], and analyzed the relationships between activities levels and the C:N:P ratios and soil-associated physical and chemical factors. The results were as follows:(1)Enzyme activities were higher in the restoration types than in the three land use types. In addition, the activities of the four enzymes, enzymatic N:P, and enzymatic C:P of pasture grassland were higher than those in the other restoration types. The βG and ALP activities in the deciduous forest were significantly higher than those in the natural restoration and evergreen forest, and NAG activity in the evergreen forest was significantly higher than that in the other three restoration types. The enzymatic N:P ratios of the evergreen-deciduous mixed forests were significantly lower than those in the other restoration types, as was the enzymatic C:P ratio of the deciduous forest. In addition, vector analysis of the enzyme activity measurement ratio showed that all land use and restoration types were limited by P.(2)The activities of the four enzymes were positively correlated with soil organic C(SOC), ammonia N(NH⁺₄-N), and nitrate N(NO₃^--N), whereas negatively correlated with total P(TP). βG activity was positively correlated with available P(AP)and ALP activity was positively correlated with total N(TN).(3)Redundancy analysis(RDA)showed that the levels of TP, NH⁺₄-N, NO₃^--N, and AP explained 38.3%, 9.5%, 9.3%, and 8.0%, respectively, of the changes in soil enzyme activities and C:N:P ratios. Based on these results, the different land use and restoration types in karst areas are shown to generally exist under the limitation of soil P, which implies that the fixation and transformation of P should be the focus of soil quality improvement in the land use development and restoration process. Furthermore, soil enzyme activities, C:P ratios, and AP contents in pasture grassland, evergreen-deciduous mixed forest, and deciduous forest were higher than those in the other land use and restoration types. The result indicates that forage and deciduous plants are important for soil nutrient cycling and should be considered in the process of karst land use and restoration.

Species abundance distribution pattern of plant communities in different terrains in subtropical karst area

2022/7/20 10:21:33

In order to explore of the species abundance distribution(SAD)pattern of plant communities under different terrains in subtropical karst area, to reveal the SAD formation mechanism of the community under different terrains, and to enrich the theory of plant community construction in this area, the arbor layer and shrub layer of plant communities under four typical landforms of ridge, trough valley, saddle and depression in Maolan karst area of Guizhou Province were used as the objects. The empirical cumulative distribution function(ECDF)was used to characterize the SAD, at the same time, the Wilcoxon rank sum test was used to analyze the differences in species abundance between different terrain. Then different ecological models were used for fitting, and Kolmogorov-Smirnov(K-S)test and Akaike Information Criterion(AIC)were used to detect model acceptance and goodness of fit. The results were as follows:(1)There were differences in the number of individuals and species in plant communities under different terrains, the number of individuals in saddles was the most, the number of species in depressions was the most, and the number of individuals and species in ridges was the least.(2)There were significant differences among shrub layers, between ridge and saddle, between ridge and depression, between saddle and trough valley, and between saddle and depression, while there were no significant differences in the SAD of arbor layers in plant communities under different terrains.(3)The SAD of the arbor layer under different terrains was well accepted by the neutral model. The ridge fitted best, but all terrains were poorly accepted by ecological models, only the ridge and saddle passed through the two niche models, and the goodness of fit was not as good as that of the neutral model. The shrub layer was also well accepted by the neutral model with the best fit of the saddle, but it was poorly accepted by the niche model, and only the depression passed the broken stick model. Overall, the arbor layer was more acceptable to the two ecological models than the shrub layer, probably because the SAD of the arbor layer had more obvious imprints of ecological processes. However, the difference in the goodness of fit of the shrub layer under different terrains is greater, which may be related to the more drastic changes of the shrub layer species to the environment. Consequently, different terrains lead to different ecological processes of community construction, and the SAD pattern gradually adapts to the terrain.