Effects of different soil and water conservation measures on plant diversity and productivity in Loess Plateau.

Many soil and water conservation measures (SWCM) have been implemented in the Loess Plateau of China, and they have an impact on ecosystems all levels and involve complicated mechanisms. Previously, studies typically focused on a single factor's effect on diversity or productivity. With this background, the current investigation embarked on an extensive study, with vegetation survey conducted in the no measure plots (NM), vegetation measure plots (VM) and engineering measure plots (EM) in the Loess Plateau of China. We used structural equation models (SEM) to explain the mechanism by which SWCM affects plant productivity and diversity. VM have direct effects on plant diversity, and EM have direct effects on soil properties and community structure. The two measures also had indirect effects on plant functional traits and community structure. The results show that the changes in plant functional traits and community structure by SWCM decreased plant diversity, whereas the increase of productivity was primarily dominated by improvements in community structure, and we conclude that variability in plant diversity and productivity across different measures on the Loess Plateau was primarily due to the responses of different plants to variable soil properties and the community responses. It was also emphasized that vegetation measures were beneficial to the increase of biomass per plant, while engineering measures were more beneficial to the growth of dominant species. These findings provide a theoretical foundation for vegetation management and restoration after the application of different SWCM.

Discriminating the impacts of vegetation greening and climate change on the changes in evapotranspiration and transpiration fraction over the Yellow River Basin.

Evapotranspiration (ET) is a vital parameter in terrestrial water-energy cycles. The transpiration fraction (TF) is defined as the ratio of transpiration (T) to evapotranspiration (ET), representing the contribution rate of vegetation transpiration to ecosystem ET. Quantifying the relative contributions of vegetation and climate change on the ET and TF dynamic is of great significance to better understand the water budget between the land and atmosphere. Here, we chose Yellow River Basin (YRB) as the study area and analyzed the spatiotemporal changes of ET, T, and TF from 1982 to 2015 using the Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model. Meanwhile, the relative contributions of vegetation and climate change to ET, T and TF change were quantified. Model evaluation showed that the PT-JPL model performs well in the simulation of ET and T. During 1982-2015, the average annual ET, T, and TF increased at a rate of 3.20 mm/a, 0.77 mm/a and 0.003/a over the YRB during 1982-2015, respectively. The regions with significant increases in ET, T and TF almost covered the whole study area except for the upper reaches of the YRB. Vegetation greening was the main factor for the increase of ET and TF in the YRB and enhanced ET and TF at a rate of 0.72 mm/a and 0.57/a, respectively, which mainly observed in the entire Loess Plateau region (over 50 % of the study area). Precipitation (PRE) was also the dominated factor contributing to the increase in ET and TF, and temperature (TEM) showed a positive correlation with the changes in ET and TF in the most areas of YRB, which jointly dominated ET changes in the upper reaches of the YRB and TF changes in the southern part of the basin. Except for the total effects, leaf area index (LAI) also indirectly promoted ET changes by affecting PRE, TEM and relative humidity (RH). While wind speed (WS) and radiation (RAD) had a relatively weak regulatory effect on the changes in ET and TF. These findings were helpful for regional water resources management and formulating water resources-sustainable vegetation restoration strategies for local government.

Contrasting patterns of community-weighted mean traits and functional diversity in driving grassland productivity changes under N and P addition.

Fertilization could influence ecosystem structure and functioning through species turnover (ST) and intraspecific trait variation (ITV), especially in nutrient limited ecosystems. To quantify the relative importance of ITV and ST in driving community functional structure and productivity changes under nitrogen (N) and phosphorous (P) addition in semiarid grasslands. In this regard, we conducted a four-year fertilizer addition experiment in a semiarid grassland on the Loess Plateau, China. We examined how fertilization affects species-level leaf and root trait plasticity to evaluate the ability of plants to manifest different levels of traits in response to different N and P addition. Also, we assessed how ITV or ST dominated community-weighted mean (CWM) traits and functional diversity variations and evaluated their effects on grassland productivity. The results showed that the patterns of plasticity varied greatly among different plant species, and leaf and root traits showed coordinated variations following fertilization. Increasing the level of N and P increased CWM_specific leaf area (CWM_SLA), CWM_leaf N concentration (CWM_LN) and CWM_maximum plant height (CWM_Hmax) and ITV predominate these CWM traits variations. As a results, increased CWM_Hmax, CWM_LN and CWM_SLA positively influenced grassland productivity. In contrast, functional divergence decreased with increasing N and P and showed negative relationships with grassland productivity. Our results emphasized that CWM traits and functional diversity contrastingly drive changes in grassland productivity under N and P addition.

Periodical Progress in Ecophysiology and Ecology of Grassland.

As one of the most important ecosystems on the planet, grasslands serve a variety of purposes in ecology, economy, culture and entertainment [...].

Agents Affecting the Plant Functional Traits in National Soil and Water Conservation Demonstration Park (China).

Plant functional traits (PFTs) can reflect the response of plants to environment, objectively expressing the adaptability of plants to the external environment. In previous studies, various relationships between various abiotic factors and PFTs have been reported. However, how these factors work together to influence PFTs is not clear. This study attempted to quantify the effects of topographic conditions, soil factors and vegetation structure on PFTs. Four categories of variables were represented using 29 variables collected from 171 herb plots of 57 sites (from different topographic and various herb types) in Xindian SWDP. The partial least squares structural equation modeling showed that the topographic conditions and soil properties also have a direct effect on plant functional traits. Among the topographic conditions, slope (SLO) has the biggest weight of 0.629, indicating that SLO contributed the most to plant functional traits and vegetation structure. Among soil properties, maximum water capacity (MWC) contributes the most and is followed by soil water content (SWC), weighted at 0.588 and 0.416, respectively. In a word, the research provides new points into the quantification of the correlation between different drivers that may be important for understanding the mechanisms of resource utilization, competition and adaptation to the environment during plant recovery.

Using Trait-Based Methods to Study the Response of Grassland to Fertilization in the Grassland in Semiarid Areas in the Loess Plateau of China.

Grassland is the dominant vegetation type in the Loess Plateau, and grassland productivity and processes are limited by nitrogen (N) and phosphorus (P). Studies have shown that productivity would change following fertilization in the grassland. The response of productivity to fertilization mainly depends on the dominant species traits. Trait-based methods provide a useful tool for explaining the variations in grassland productivity following fertilization. However, the relative contribution of plant functional traits to grassland productivity under N and P addition in the Loess Plateau is not clear. We measured aboveground biomass (AGB) and leaf N content (LN), leaf P content (LP), leaf N/P ratio (LN/P), specific leaf area (SLA), leaf tissue density (LTD), leaf dry matter content (LDMC), and maximum plant height (Hmax) to study how these plant functional traits regulate the relative biomass of different species and grassland productivity following fertilization. Our results showed, that under different nutrient addition levels, the linkages between plant functional traits and the relative biomass of different species were different. Community AGB was positively related to community-weighted mean LN (CWM_LN), CWM_LN/P, CWM_SLA, and CWM_Hmax, but negatively related to CWM_LTD and CWM_LDMC. Dominant species traits largely determined grassland productivity, in line with the mass ratio hypothesis. These findings further highlight the close linkages between community-level functional traits and grassland productivity. Our study contributes to the mechanisms underlying biodiversity-ecosystem function relationships and has significance for guiding semiarid grassland management.

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With the exacerbating disturbances of climate changes and human activities to terrestrial ecosystems, more and more studies realize that ecosystems are at the risk of shifts without warning in structural and functional states and recovery from perturbations require more time. Developing an early warning model to identify critical transition and understanding its ecological mechanism of typical ecosystems have become hotspot in ecological researches. At present, based on theoretical and experimental researches across multiple spatiotemporal scales, a variety of theoretical frameworks and indicators of early warning signals (EWSs) were proposed to signal terrestrial ecosystem critical transition. Here, in order to more thoroughly understand and construct theoretical frameworks and indicators of early warning signals, we reviewed advances in critical transitions from aspects of theoretical methods and processing mechanisms. Catastrophe theory and critical slowing down (CSD) are the two basic theories for early-warning ecosystem state transitions. Self-organization and feedback mechanisms are the primary ecological mechanisms to shape alternative stable state. Understanding cascade effects networks (CENet) among biological and environmental elements, and clarifying the equilibrium relationships between input and output of key ecosystem parameters are theoretical foundation of critical transition model. These theoretical cognitions could provide useful references to early warning of ecosystem disasters, ecological environment management and restoration.

Different biomass production and soil water patterns between natural and artificial vegetation along an environmental gradient on the Loess Plateau.

Loess Plateau (LP) is a vulnerable and climate-sensitive ecoregion. With the implementation of "Grain for Green" project (GGP), the vegetation cover has largely improved, while the contradiction between overconsumption of soil water and sustainability of restored vegetation is increasingly prominent, and further threatening the ecosystem sustainability and socioeconomic development. Understanding the different responses of relations of biomass production and soil water regimes between natural and artificial vegetation along environmental gradient will be crucial for sustainability of restored vegetation on the LP. Here, aboveground biomass (AGB) and soil water content (SWC) of natural and artificial vegetation were measured in steppe, forest-steppe and forest zone from 2008 to 2017 on the Yanhe River catchment. The results showed that artificial vegetation consumed more soil water than natural vegetation in steppe and forest-steppe zone, while it did not over consume soil water in forest zone. The AGB of natural vegetation in forest zone was significantly higher than that in steppe and forest-steppe zone. Steppe zone had serious overload of artificial vegetation (overload ratio: 5.35), while no overload occurred in forest zone. So, we suggest a cessation of artificial vegetation expansion in steppe zone. In steppe zone, planting artificial vegetation increased competition intensity between AGB and SWC, and the relative benefit tended to be AGB, their competition intensity was the highest. In forest zone, the trade-off relationship between AGB and SWC had no significant difference between natural and artificial vegetation, and the competition intensity between the AGB and SWC was the weakest. Optimal vegetation restoration approach would maintain the balance between vegetation restoration and soil water. To obtain social and ecological sustainability on the LP, vegetation suitability and suitable management along different environmental gradients should be considered and identified in the future revegetation project.

Quantifying Leaf Trait Covariations and Their Relationships with Plant Adaptation Strategies along an Aridity Gradient.

A trait-based approach is an effective way to quantify plant adaptation strategies in response to changing environments. Single trait variations have been well depicted before; however, multi-trait covariations and their roles in shaping plant adaptation strategies along aridity gradients remain unclear. The purpose of this study was to reveal multi-trait covariation characteristics, their controls and their relevance to plant adaptation strategies. Using eight relevant plant functional traits and multivariate statistical approaches, we found the following: (1) the eight studied traits show evident covariation characteristics and could be grouped into four functional dimensions linked to plant strategies, namely energy balance, resource acquisition, resource investment and water use efficiency; (2) leaf area (LA) together with traits related to the leaf economic spectrum, including leaf nitrogen content per area (Narea), leaf nitrogen per mass (Nmass) and leaf dry mass per area (LMA), covaried along the aridity gradient (represented by the moisture index, MI) and dominated the trait-environmental change axis; (3) together, climate, soil and family can explain 50.4% of trait covariations; thus, vegetation succession along the aridity gradient cannot be neglected in trait covariations. Our findings provide novel perspectives toward a better understanding of plant adaptations to arid conditions and serve as a reference for vegetation restoration and management programs in arid regions.

Identification of Fungal Dynamics Associated With Black Locust Leaves Mineralization and Their Correlations With Physicochemical Factors.

In this study, the fungal dynamics associated with black locust (BL) mineralization and its correlation with various environmental factors were evaluated across three different vegetation types along a gradient of temperature and humidity. The results confirmed that Ascomycota and Basidiomycota were the dominant phyla in each habitat, with average relative abundance of 86.57 and 11.42%, respectively. But both phylum abundance varied significantly among different BL leaves' decomposing habitats. Black locust changed the most significantly in the forest habitat and the least in the steppe. In addition, the litter characteristics of BL decreased with total carbon and total nitrogen mineralization and underground water level in water-rich region, while this result was significantly consistent with the fungal diversity. Co-occurrence network studies revealed that significant correlations were found between fungal community composition and environmental factors, the decrease of underground water level influence the fungal structure in forest habitat. Finally, the present study results provide important insights about the biological invasion of new ecosystems.

Drought-Induced Carbon and Water Use Efficiency Responses in Dryland Vegetation of Northern China.

Given the context of global warming and the increasing frequency of extreme climate events, concerns have been raised by scientists, government, and the public regarding drought occurrence and its impacts, particularly in arid and semi-arid regions. In this paper, the drought conditions for the forest and grassland areas in the northern region of China were identified based on 12 years of satellite-based Drought Severity Index (DSI) data. The impact of drought on dryland vegetation in terms of carbon use efficiency (CUE) and water use efficiency (WUE) were also investigated by exploring their correlations with DSI. Results indicated that 49.90% of forest and grassland experienced a dry trend over this period. The most severe drought occurred in 2001. In general, most forests in the study regions experienced near normal and wet conditions during the 12 year period. However, grasslands experienced a widespread drought after 2006. The forest CUE values showed a fluctuation increase from 2000 to 2011, whereas the grassland CUE remained steady over this period. In contrast, WUE increased in both forest and grassland areas due to the increasing net primary productivity (NPP) and descending evapotranspiration (ET). The CUE and WUE values of forest areas were more sensitive to droughts when compared to the values for grassland areas. The correlation analysis demonstrated that areas of DSI that showed significant correlations with CUE and WUE were 17.24 and 10.37% of the vegetated areas, respectively. Overall, the carbon and water use of dryland forests was more affected by drought than that of dryland grasslands.

Soil Moisture Availability at Early Growth Stages Strongly Affected Root Growth of Bothriochloa ischaemum When Mixed With Lespedeza davurica.

Rainfall is the main resource of soil moisture in the semiarid areas, and the altered rainfall pattern would greatly affect plant growth and development. Root morphological traits are critical for plant adaptation to changeable soil moisture. This study aimed to clarify how root morphological traits of Bothriochloa ischaemum (a C4 herbaceous species) and Lespedeza davurica (a C3 leguminous species) in response to variable soil moisture in their mixtures. The two species were co-cultivated in pots at seven mixture ratios under three soil water regimes [80% (HW), 60% (MW), and 40% (LW) of soil moisture field capacity (FC)]. At the jointing, flowering, and filling stages of B. ischaemum, the LW and MW treatments were rewatered to MW or HW, respectively. At the end of growth season, root morphological traits of two species were evaluated. Results showed that the root morphological response of B. ischaemum was more sensitive than that of L. davurica under rewatering. The total root length (TRL) and root surface area (RSA) of both species increased as their mixture ratio decreased, which suggested that mixed plantation of the two species would be beneficial for their own root growth. Among all treatments, the increase of root biomass (RB), TRL, and RSA reached the highest levels when soil water content increased from 40 to 80% FC at the jointing stage. Our results implied that species-specific response in root morphological traits to alternated rainfall pattern would greatly affect community structure, and large rainfall occurring at early growth stages would greatly increase their root growth in the semiarid environments.

The impacts of land conversion and management measures on the grassland net primary productivity over the Loess Plateau, Northern China.

In the 1990s, the Chinese government began implementation of a series of national-scale restoration programs to combat environmental degradation. As one of most important arid and semiarid regions of China, the Loess Plateau has attracted attention related to the effectiveness of these initiatives. The present study analyzed land use and cover change (LUCC) of the grassland in the Loess Plateau and the consequent change in net primary productivity (NPP) based on a consecutive land use data derived from the European Space Agency Climate Change Initiative land cover maps and the CASA (Carnegie-Ames-Stanford Approach) model driven by MODIS-NDVI data. The contributions of climate variation and human activities (including land conversion and management measures) to these changes were also quantitatively differentiated. The results indicated that the area of the Loess Plateau grassland experienced a net increase of 0.43 × 104 km2 over the study period. The total NPP of the Loess Plateau grassland increased by 11,325.13 Gg C·yr-1, of which the human activities and climate variation were responsible for 78.45% and 21.55%, respectively. The land conversion reduced the grassland NPP by 308.60 Gg C·yr-1, whereas management measures increased the NPP by 9197.97 Gg C·yr-1 in the otherwise unmodified grassland. Overall, ecological restoration programs have effectively increased grassland NPP in the Loess Plateau. However, human activities played both positive and negative impacts in this process.

Mapping the climatic suitable habitat of oriental arborvitae (Platycladus orientalis) for introduction and cultivation at a global scale.

Oriental arborvitae (Platycladus orientalis) is an important afforestation and ornamental tree species, which is native in eastern Asian. Therefore, a global suitable habitat map for oriental arborvitae is urgently needed for global promotion and cultivation. Here, the potential habitat and climatic requirements of oriental arborvitae at global scale were simulated using herbariums data and 13 thermal-moisture variables as input data for maximum entropy model (MaxEnt). The simulation performance of MaxEnt is evaluated by ten-fold cross-validation and a jackknife procedure. Results show that the potential habitat and climate envelop of oriental arborvitae can be successfully simulated by MaxEnt at global scale, with a mean test AUC value of 0.93 and mean training AUC value of 0.95. Thermal factors play more important roles than moisture factors in controlling the distribution boundary of oriental arborvitae's potential ranges. There are about 50 countries suitable for introduction and cultivation of oriental arborvitae with an area of 2.0 × 10(7) km(2), which occupied 13.8% of land area on the earth. This unique study will provide valuable information and insights needed to identify new regions with climatically suitable habitats for cultivation and introduction of oriental arborvitae around the world.

A novel approach for modelling vegetation distributions and analysing vegetation sensitivity through trait-climate relationships in China.

Increasing evidence indicates that current dynamic global vegetation models (DGVMs) have suffered from insufficient realism and are difficult to improve, particularly because they are built on plant functional type (PFT) schemes. Therefore, new approaches, such as plant trait-based methods, are urgently needed to replace PFT schemes when predicting the distribution of vegetation and investigating vegetation sensitivity. As an important direction towards constructing next-generation DGVMs based on plant functional traits, we propose a novel approach for modelling vegetation distributions and analysing vegetation sensitivity through trait-climate relationships in China. The results demonstrated that a Gaussian mixture model (GMM) trained with a LMA-Nmass-LAI data combination yielded an accuracy of 72.82% in simulating vegetation distribution, providing more detailed parameter information regarding community structures and ecosystem functions. The new approach also performed well in analyses of vegetation sensitivity to different climatic scenarios. Although the trait-climate relationship is not the only candidate useful for predicting vegetation distributions and analysing climatic sensitivity, it sheds new light on the development of next-generation trait-based DGVMs.

[Trait-based responses and adaptation of Artemisia sacrorum to environmental changes].

The paper focused on Artemisia sacrorum in the stable natural plant community in three vegetation zones (forest, forest steppe and steppe) in the Yanhe River catchment. The following plant functional traits were measured at each sample site, i.e., specific leaf area (SLA), leaf tissue density (LTD), leaf nitrogen concentration (LNC), leaf phosphorus concentration (LPC), leaf nitrogen phosphorus ratio (LNP), specific root length (SRL), root tissue density (RTD), root nitrogen concentration (RNC), root phosphorus concentration (RPC) and root nitrogen phosphorus ratio (RNP). These 10 plant functional traits were chosen because they were easily measurable and adequately reflected plant survival strategies. We analyzed intraspecific differences in A. sacrorum functional traits in the different habitat zones, and the influence of climate and terrain factors on A. sacrorum functional traits. We also studied the relationships among A. sacrorum plant functional traits. The results showed that some A. sacrorum functional traits were significantly different among sample sites, such as LPC, LNP, SRL, RTD and RNP, while the other 5 functional traits had no significant differences. The functional traits were not significantly different between sites with different slopes and aspects. SLA was very significantly negatively correlated with LTD, SRL was significantly negatively correlated with RTD and RNP, RTD was significantly positively correlated with RNC and RNP, and there were no significant relationships among LTD, LNC and LNP and the other functional traits. This showed that A. sacrorum adapted to the environment by coordinating adjustment among leaf and root functional traits. Different climate factors had different effects on plant traits, with the effects of mean annual precipitation > mean annual temperature > annual average evaporation capacity.

Evaluating sustainability of cropland use in Yuanzhou county of the Loess plateau, China using an emergy-based ecological footprint.

Evaluating the sustainability of cropland use is essential for guaranteeing a secure food supply and accomplishing agriculture sustainable development. This study was conducted in the ecologically vulnerable Loess Plateau region of China to evaluate the sustainability of cropland use based on an ecological footprint model that integrates emergy analysis. One modified method proposed in 2005 is known as the emergetic ecological footprint (EEF). We enhanced the method by accounting for both the surface soil energy in the carrying capacity calculation and the net topsoil loss for human consumption in the EF calculation. This paper evaluates whether the cropland of the study area was overloaded or sustainably managed during the period from 1981 to 2009. Toward this end, the final results obtained from EEF were compared to conventional EF and previous methods. The results showed that the cropland of Yuanzhou County has not been used sustainably since 1983, and the conventional EF analysis provided similar results. In contrast, a deficit did not appear during this time period when previous calculation methods of others were used. Additionally, the ecological sustainable index (ESI) from three models indicated that the recently used cropland system is unlikely to be unsustainable.

[Relationships among leaf traits and their expression in different vegetation zones in Yanhe River basin, Northwest China].

This article selected zonal plant communities as the research objects in different vegetation zones in Yanhe River basin. We measured six leaf traits of the dominant species and main accompanying species in each community, and then analyzed the relationships and their changes along with environmental gradients between these traits in order to understand the plant adaptation strategies to the environment changes. The results showed that the specific leaf area was significantly negatively correlated to leaf tissue density, area-based leaf nitrogen and phosphorus concentrations, and significantly positively correlated to mass-based leaf phosphorus concentration. Both the scaling relationships among these traits and plant life strategies were different among the three vegetation zones, the scaling-dependent relationship between leaf tissue density and specific leaf area was stronger in steppe and forest-steppe zones than in forest zone, but the correlations among area-based leaf nitrogen/phosphorus concentrations and specific leaf area and leaf tissue density were more significant in forest zone than in steppe zone. In the arid grassland and forest-steppe zone, plants give priority to defensive and stress resistance strategies, and in relatively moist nutrient-rich forest zone, plants give priority to fast growth and resource optimization allocation strategies.

[Responses of plant functional traits to micro-topographical changes in hilly and gully region of the Loess Plateau, China].

Plant functional traits are closely tied to the performance of plants in specific microenvironments, and reflect their ability to adapt to those microenvironments. In areas with complex topography, analyzing the responses of plant functional traits to microtopographical changes is crucial to understanding the adaptive strategies of plants in diverse environments. This paper analyzed fluctuations in soil nutrients as well as correlations between plant functional traits and changes in topography at the family and community levels in selected natural vegetation communities in the foreststeppe zone of the loess hilly and gully region in Loess Plateau of China. Significant differences in plant functional traits were primarily driven by the phylogenetic background or species composition of the community. Slope aspect exerted less impact while slope positions had no significant effect on plant traits at the community level. No significant changes in plant functional traits were observed with changes in topography at the community level. However, leaf nitrogen and root nitrogen contents of Leguminous and Compositae species differed significantly With slope positions. The root tissue density of Graminaceous species differed significantly with slope positions. Root density exhibited significant positive correlations with soil nutrient and carbon contents at the community level. Both leaf nitrogen and root nitrogen contents of Leguminous species were positively correlated with soil phosphorus content, while leaf nitrogen and root nitrogen contents of both Graminaceous and Compositae species were significantly positively related to soil nitrogen content. The results demonstrate the different responses of species of different families to changes in micro-topography and their distinctive adaptive strategies to the environment.

Soil nutrient assessment based on attribute recognition model in the Loess Plateau of China.

Soil fertility is important factors for growth and productivity of vegetation. The relationship between vegetation and soil fertility deserves attention due to its scientific importance and practical applications. However, the effects of soil fertility on vegetation development and succession are poorly documented. Here we study soil fertility in Yanhe watershed at northern Shaanxi on five different land uses, namely shrubland, farmland, natural grassland, woodland, and artificial grassland, and in soil under restoration for 5, 10, 15, 20, and 25. Attribute recognition model based on entropy weight was used to evaluate the soil fertility of typical region in the Loess Plateau of China, which contained 52 soil samples with 6 physical and chemical indexes, including soil organic matter, soil total nitrogen, total phosphorus, etc. The results show that (1) Land use has an obvious effect on soil bulk density, total porosity and capillary porosity of surface layers, but not significant in the subsurface layer; (2) SOM, Ntotal, Nhydro and Kavail are the most in shrubland and woodland while Ptotal and Pavail in farmland, respectively; (3) Vegetation succession on eroded soil result in significant changing of soil fertility; and (4) Vegetation succession on eroded soil result in significant changing of soil fertility.