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Highlights • Delaying sowing promoted forage maize, Sudan grass used water from deep layers at jointing, flowering and maturity. • Delaying sowing promoted foxtail millet and Japanese millet absorbed deep water at flowering and maturity. • Plant water use in a semi-arid environment is controlled by both environment and growth stage. Abstract Plant water use strategies are crucial for fodder production in semi-arid environments, with implications for food supply, livestock products and social sustainability in a global warming environment. This study aimed to determine the effect of phenology and sowing date on water use in four annual forage crops on the Loess Plateau of China. Hydrogen and oxygen isotope ratios (δD and δ18O) measured soil water in different layers (0–1.2 m), xylem water at jointing, flowering and maturity, and rainwater. The IsoSource model was used to calculate the relative contribution of soil water to plant water use in the shallow (0–0.1 m), middle (0.1–0.6 m) and deep (0.6–1.2 m) layers. As the forage crops grew, more water was absorbed from deeper layers. Delaying sowing up to four weeks could promote forage maize (Zea mays), Sudan grass (Sorghum sudanense Stapf.) used water from deep layers at all measured growth stages (jointing, flowering, and maturity). Foxtail millet (Setaria italica) and Japanese millet (Echinochloa crus-galli var. frumentacea) absorbed deep water at flowering and maturity. Further, maize, Sudan grass, and foxtail millet used more water at flowering while Japanese millet used more at maturity. The distinct water use patterns of the four crops at different growth stages and sowing dates showed that plant water use in a semi-arid environment is controlled by both environment and growth stage. Delaying sowing might be an efficient way of coping with water stress caused by unpredictable rainfall by using water from deeper layers to reduce the risk of yield losses. Our results provide a reference for agricultural water management under global warming and sustainability in rainfed farming systems. [ABSTRACT FROM AUTHOR]

Highlights • Calibrating parameters is necessary for dynamic vegetation model in local scale. • Potential forest areas will decrease, while potential steppe areas will increase. • Existing land use pattern should be adjusted to adapt to climate change. • Shrubs have larger area and higher habitat suitability than forests. • Results could guide decision makers in developing effective revegetation plans. Abstract Global concern about the restoration of vegetation ecosystems has recently increased. Potential natural vegetation (PNV) and climate adaptation concepts should be integrated into revegetation programs to achieve sustainable ecosystems. The Yanhe Basin in the Loess Plateau of China (7687 km2) has been subjected to intense human activity for centuries. It was selected as the study area because vegetation degradation and restoration are occurring there. The objectives of this study were to (1) evaluate whether the current vegetation pattern is appropriate, and (2) provide a restoration plan for future revegetation programs based on PNV and habitat suitability patterns simulated by the dynamic vegetation model LPJ-GUESS. Current work focused on the parameter calibration and high-resolution climate data of the model over the study area. The comparisons of model performances in the PNV pattern and productivity indicated that parameter calibration was necessary for the model application. PNV of the Yanhe Basin may shift by 21.37–29.67% from 1981–2010 to 2071–2100, mainly in the southern part. Forests may decrease and steppes may increase as the climate becomes drier in the future. Comparisons between an existing land use map and the current PNV pattern indicated that only 40.8% of the forestland was coincident with the current PNV pattern, whereas grassland was a more suitable vegetation type for the rest of the terrain. In contrast, 83.1% of the grassland aligned with the current PNV pattern. Therefore, 16.9% remains to be forested. Current forestland and grassland patterns should be adjusted to cope with future climate change. Broadleaf summer-green shrubs covered a larger area and had higher habitat suitability than forests; they might be the most suitable woody plants for revegetation of the Yanhe Basin. The applied research approach could be extended to other regions undergoing similar revegetation programs and help promote sustainable vegetation management. [ABSTRACT FROM AUTHOR]

Quantifying and predicting variation in gross primary productivity (GPP) is important for accurate assessment of the ecosystem carbon budget under global change. Scaling traits to community scales for predicting ecosystem functions (i.e., GPP) remain challenging, while it is promising and well appreciated with the rapid development of trait-based ecology. In this study, we aim to integrate multiple plant traits with the recently developed trait-based productivity (TBP) theory, verify it via Bayesian structural equation modeling (SEM) and complementary independent effect analysis. We further distinguish the relative importance of different traits in explaining the variation in GPP. We apply the TBP theory based on plant community traits to a multi-trait dataset containing more than 13,000 measurements of approximately 2,500 species in Chinese forest and grassland systems. Remarkably, our SEM accurately predicts variation in annual and monthly GPP across China (R2 values of 0.87 and 0.73, respectively). Plant community traits play a key role. This study shows that integrating multiple plant functional traits into the TBP theory strengthens the quantification of ecosystem primary productivity variability and further advances understanding of the trait-productivity relationship. Our findings facilitate integration of the growing plant trait data into future ecological models. Integration of plant functional traits into trait-based productivity theory helps quantify primary productivity in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

• Effect of sowing date on biomass partition varied with forage crop species. • Aboveground biomass at flowering was dependent on rainfall and solar radiation. • Aboveground biomass at maturity more reliant on temperature and rainfall. • Allometric approach should be used in the analysis of allocation pattern. Biomass production and partitioning are important for crop production and is influenced by environmental conditions. Sowing date can profoundly influence biomass production and portioning in crop plants depending upon the local climatic conditions. However, the accumulation of biomass in different plant components in annual forages in response to changes in sowing date has not been quantified, especially for semiarid farming systems. A field experiment was conducted during 2011–2013 to investigate how sowing date (early, mid, late) influences biomass partitioning and the interrelationships with environments in four warm-season annual crops in the Loess Plateau of China. The aboveground biomass of all four crops was more reliant on rainfall and solar radiation at flowering and temperature and rainfall at maturity. Solar radiation, rainfall, and temperature had a combined effect on belowground biomass (0–0.3 m), depending on the forage crop. Reductions in biomass in the late-sown treatment were mostly attributed to plant size; the 'allometry' among plant components did not change. The changes of shoot: root and leaf: stem ratios were related to the relationship between biomass accumulation and rainfall, temperature and intercepted radiation. It is evident that dry matter allocation patterns in crops must be analyzed using a dynamic approach (allometry) and relate with environmental conditions, rather than a static approach using ratios. The results from this study provide references for crop management in forage production and breeding in semiarid areas. [ABSTRACT FROM AUTHOR]

Complex systems can undergo abrupt state transitions near critical points. Theory and controlled experimental studies suggest that the approach to critical points can be anticipated by critical slowing down (CSD), that is, a characteristic slowdown in the dynamics. The validity of this indicator in field ecosystems, where stochasticity is important in driving transitions, remains unclear. We analyze long-term data from a dryland ecosystem in the Shapotou region of China and show that the ecosystem underwent an abrupt transition from a nearly bare to amoderate grass cover state. Prior to the transition, the systemshowed no (or weak) signatures of CSD but exhibited expected increasing trends in the variability of the grass cover, quantified by variance and skewness. These surprising results are consistent with the theoretical expectation of stochastically driven abrupt transitions that occur away from critical points; indeed, a driver of vegetation--annual rainfall--showed rising variance prior to the transition. Our study suggests that rising variability can potentially serve as a leading indicator of stochastically driven transitions in real-world ecosystems. [ABSTRACT FROM AUTHOR]

• Soil fungal community shifted from symbiotroph and saprotroph species towards pathotroph species with increased soil nutrients after two decades along a shrub plantation chronosequence. • Changes in microbial community composition and more fragmented network structure preceded the degradation of shrub physiology and biomass after 40 years. • A breakdown in soil microbial community structure can be an early warning sign of declines in shrub productivity and land degradation. Large-scale restoration is intended to promote ecological recovery. Improvements in plant and microbial conditions, however, may slow or even reverse in late succession. To better understand long-term restoration outcomes and underlying drivers of successional pathways, we tracked plant, bacterial and fungal, and soil conditions across a 40-year shrub plantation that was intended to stabilize desertified land in northern China. We found that planted Haloxylon ammodendron shrubs developed and then subsequently became degraded after 30–40 years. Bacterial abundance and α-diversity were much higher than those of fungi, but no significant differences in composition and structure were found in different plantation ages. In contrast, the dominant taxa of fungal communities shifted from symbiotroph and saprotroph species towards pathotroph species with increased soil nutrients in the plantation chronosequence after two decades. The changes in fungal dominant species led to a transition in microbial network structure and function, with an increase in negative linkages among taxa that began in the middle stages of succession. Changes in fungal community structure had direct and indirect negative effects on shrub leaf physiology, root activity, and biomass. Our results highlight the preceding role of a breakdown in soil microbial community composition and network structure on the degradation of shrub performance in long-term desert succession. Our study emphasizes the importance of understanding soil-microbial-plant linkages on restoration outcomes, and mechanisms that can slow or reverse the recovery of ecosystems. [ABSTRACT FROM AUTHOR]

Straw return has been widely used to increase SOC storage globally, but such C accrual is frequently constrained by other nutrients which are needed to maintain soil ecological stoichiometry balance. However, the impact of fertilization on SOC stocks under straw return remains unexplored at broad spatial scales. We constructed a national-scale dataset to explore the fertilization effect on SOC stocks (0–20 cm) under straw return and identified the dominant drivers and pathways in upland and paddy systems across China. On average, straw return enhanced SOC stocks and sequestration rate by 1.74 Mg C ha−1 and 0.27 Mg C ha−1 y−1 relative to straw removal (CK). Yet, straw co-applied with nutrient enrichment further increased SOC stock and sequestration rate by 0.81 Mg C ha−1 and 0.12 Mg C ha−1 y−1, compared to straw return only. These results indicated a general nutrient limitation on SOC sequestration under straw return. The fertilization effect on SOC stocks varied greatly across nutrient enrichment types and cropping systems, with greater soil C gain occurring under balanced fertilization (i.e., NPK) and more in uplands than in paddy fields. In the uplands, SOC sequestration with fertilization was positively correlated with increased belowground biomass. In paddy fields, however, improved biomass with fertilization did not translate into increased SOC accumulation, owing to the co-limitations of soil acidification and initial SOC. We further clarified the differential pathways by which chemical fertilization altered SOC stocks, i.e., productivity pathway in uplands but decomposition pathway in paddy fields. These mechanistic insights on the fertilization control over SOC can help us optimize the context-specific integrated straw and fertilization management strategies for greater SOC sequestration, and also inform the development of soil C projections by incorporating fertilization management into biogeochemical models in agroecosystems. [Display omitted] • Nutrient limitation of SOC stocks under straw return was assessed across China. • Balanced fertilization promoted SOC sequestration under straw return. • SOC gain due to fertilization was much higher in uplands than in paddy fields. • Improved productivity with fertilization did not translate into increased SOC in paddies. • Fertilization modified SOC stocks via differential pathways across cropping systems. [ABSTRACT FROM AUTHOR]

• Land degradation can be reversed by desert-oasis protection systems. • Protection increased plant cover, soil nutrients, and diminished wind erosion. • Soil salinity, sodicity, and desiccation increased in well protected plantations. • Protection benefit should be weighed against unintended environmental consequences. Oasis-protection systems are created globally to reverse land degradation in drylands and improve ecosystem condition. This study assessed the effects of a 40-year oasis-protection system on soil physicochemical and plant community properties along a gradient from prohibited grazing to fenced shrublands, to shrub- and tree plantation belts in arid northwestern China. We found that compared with shifting dunes in unprotected desert settings, the wind velocity and sand transportation rate decreased by 75 and 98% when spring storms passed through the most protected shrub- and tree- plantations in the oasis-protection system, respectively. The fraction of silt and clay content, and soil carbon, total nitrogen, and total phosphorus significantly increased along the protection gradient, and reached their highest levels at the most protected belts. Meanwhile, an annual herbaceous plant community developed, and the densities, covers, and biomasses of herbaceous plant species increased with soil nutrients along the gradient. However, a significant increase in soil salinity, sodicity, and desiccation occurred at the shrub- and tree plantation belts, and shrub and tree species introduced in the plantations failed to regenerate after 40 years. Our results demonstrate that the positive effects of oasis-protection systems need to be weighed against the long-term negative consequences of soil salt accumulation and desiccation that can occur in frequently used shrub- and tree plantations, which limits future plant regeneration and ecosystem recovery. [ABSTRACT FROM AUTHOR]