Intermediate human activities maximize dryland ecosystem services in the long-term land-use change: Evidence from the Sangong River watershed, northwest China.

Human activities cause widespread changes in landscape composition, which can affect ecosystem services produced by these landscapes. It is usually believed that ecosystem services can be maximized only when we eliminate all human activities. However, this belief is not the case, at least in dryland ecosystems. Here, a gradient of human activity intensity was used to investigate changes in the value of ecosystem services over 30-years of land-use change between 1990 and 2020 in the arid Sangong River watershed of northwest China. Spatial analyses were performed to determine how the value of dryland ecosystem services changed with human activity intensity. Stepwise regressions and linear programming models were also performed to examine how to optimize the value of ecosystem services (i.e., regulating services, provisioning services, supporting services, and cultural services). We found that landscapes of the Sangong River watershed became increasingly fragmented and that human activities gradually intensified, but the value of ecosystem services fluctuated rather than linearly decreasing over the past 30 years. Specifically, a unimodal relationship was observed between human activities and ecosystem services. The peak value of ecosystem services was 5799 USD ha-1 yr-1 under intermediate human activity intensity (i.e., human footprint index ranged from 0.2 to 0.4 at a scale of one). Gross domestic product (GDP) per capita, population, and water consumption were the three most important driving factors of human activities and ecosystem services. Our results suggest that intermediate human activities may maximize dryland ecosystem services in long-term land-use change at the watershed scale, and highlight the importance of regulating economic development, population, and water consumption for the management of dryland ecosystem services.

Construction of a multicontrol sterility system for a maize male-sterile line and hybrid seed production based on the ZmMs7 gene encoding a PHD-finger transcription factor.

Although hundreds of genetic male sterility (GMS) mutants have been identified in maize, few are commercially used due to a lack of effective methods to produce large quantities of pure male-sterile seeds. Here, we develop a multicontrol sterility (MCS) system based on the maize male sterility 7 (ms7) mutant and its wild-type Zea mays Male sterility 7 (ZmMs7) gene via a transgenic strategy, leading to the utilization of GMS in hybrid seed production. ZmMs7 is isolated by a map-based cloning approach and encodes a PHD-finger transcription factor orthologous to rice PTC1 and Arabidopsis MS1. The MCS transgenic maintainer lines are developed based on the ms7-6007 mutant transformed with MCS constructs containing the (i) ZmMs7 gene to restore fertility, (ii) α-amylase gene ZmAA and/or (iii) DNA adenine methylase gene Dam to devitalize transgenic pollen, (iv) red fluorescence protein gene DsRed2 or mCherry to mark transgenic seeds and (v) herbicide-resistant gene Bar for transgenic seed selection. Self-pollination of the MCS transgenic maintainer line produces transgenic red fluorescent seeds and nontransgenic normal colour seeds at a 1:1 ratio. Among them, all the fluorescent seeds are male fertile, but the seeds with a normal colour are male sterile. Cross-pollination of the transgenic plants to male-sterile plants propagates male-sterile seeds with high purity. Moreover, the transgene transmission rate through pollen of transgenic plants harbouring two pollen-disrupted genes is lower than that containing one pollen-disrupted gene. The MCS system has great potential to enhance the efficiency of maize male-sterile line propagation and commercial hybrid seed production.

Quantifying the effects of precipitation exclusion and groundwater drawdown on functional traits of Haloxylon ammodendron - How does this xeric shrub survive the drought?

The increasing frequency of drought and decline in groundwater levels are causing ecophysiological changes in woody plants, particularly in desert ecosystems in arid regions. However, the combined effects of meteorological and hydrological droughts on perennial desert plants, especially phreatophytes, remain poorly understood. To address this knowledge gap, we conducted a 5-year precipitation exclusion experiment at two sites with contrasting groundwater depths in the Gurbantunggut Desert located in northwest China. Our study aimed to investigate the impacts of precipitation exclusion and groundwater depth decline on multiple traits of H. ammodendron. We found that long-term precipitation exclusion enhanced midday leaf water potential, stomatal conductance, chlorophyll content, root nonstructural carbohydrates concentration, leaf starch concentration, but decreased water use efficiency. Groundwater drawdown decreased predawn and midday leaf water potentials, maximum net photosynthetic rate, stomatal conductance, Huber value, stem water δ18O, but enhanced water use efficiency and branch nonstructural carbohydrates concentration. A combination of precipitation exclusion and groundwater depth decline reduced Huber value, but did not show exacerbated effects. The findings demonstrate that hydrological drought induced by groundwater depth decline poses a greater threat to the survival of H. ammodendron than future changes in precipitation.

Within-crown plasticity of hydraulic properties influence branch dieback patterns of two woody plants under experimental drought conditions.

In recent year, widespread declines of Populus bolleana Lauche trees (P. bolleana, which dieback from the top down) and Haloxylon ammodendron shrubs (H. ammodendron, which dieback starting from their outer canopy) have occurred. To investigate how both intra-canopy hydraulic changes and plasticity in hydraulic properties create differences in vulnerability between these two species, we conducted a drought simulation field experiment. We analyzed branch hydraulic vulnerability, leaf water potential (Ψ), photosynthesis (A), stomatal conductance (gs), non-structural carbohydrate (NSCs) contents and morphological traits of the plants as the plants underwent a partial canopy dieback. Our results showed that: (1) the hydraulic architecture was very different between the two life forms; (2) H. ammodendron exhibited a drought tolerance response with weak stomatal control, and thus a sharp decline in Ψ while P. bolleana showed a drought avoidance response with tighter stomatal control that maintained a relatively stable Ψ; (3) the Ψ of H. ammodendron showed relative consistent symptoms of drought stress with increasing plant stature, but the Ψ of P. bolleana showed greater drought stress in higher portions of the crown; (4) prolonged drought caused P. bolleana to consume and H. ammodendron to accumulate NSCs in the branches of their upper canopy. Thus, the prolonged drought caused the shoots of the upper canopy of P. bolleana to experience greater vulnerability leading to dieback of the upper branches first, while all the twigs of the outer canopy of H. ammodendron experienced nearly identical degrees of vulnerability, and thus dieback occurred uniformly. Our results indicate that intra-canopy hydraulic change and their plasticity under drought was the main cause of the observed canopy dieback patterns in both species. However, more work is needed to further establish that hydraulic limitation as a function of plant stature was the sole mechanism for causing the divergent canopy dieback patterns.

[Effects of groundwater depth on functional traits of young Haloxylon ammodendron.] / 地下水埋深对幼龄梭梭功能性状的影响.

Groundwater is an important water source for phreatophytic shrubs in arid desert areas. In order to understand the impacts of groundwater depth on functional traits of phreatophytic shrubs, two groups of groundwater levels (2 and 3.5 m) were set up using lysimeter with automatic water replenishing instrument. We measured hydraulic traits, gas exchange characteristics, and root morphological parameters of young Haloxylon ammodendron during the growing season. The results showed that predawn assimilating branch water potential, osmotic potential at full turgor, and root length ratio of young H. ammodendron in the groundwater depth of 3.5 m were lower by 48.2%, 41.5% and 56.7% than that under groundwater depth of 2 m, respectively, while maximum net photosynthetic rate of late growing season, root volume, specific root length and specific root area of fine root were 75.7%, 41.0%, 273.7% and 67.7% higher, respectively. Midday water potential and water content of assimilating branch tended to decrease first in the early growing season and then increase in the late growing season. Root distribution of young H. ammodendron along soil profile showed a significant positive correlation between the average root diameter and soil depth, while the proportion of fine root surface area showed a significant negative correlation with soil depth at both groundwater levels. There was synergy of aboveground assimilating branch hydraulic traits and photosynthetic capacity with belowground root morphological traits in young H. ammodendron. Under the condition of increasing groundwater depth, young H. ammodendron adopted the ecological strategies of reducing predawn assimilating branch water potential and osmotic potential at full turgor, and increasing root diameter and length to enhance water deficit tolerance and expanding the area of water uptake to sustain their survival.