Li-Song Tang

Distinguishing the biomass allocation variance resulting from ontogenetic drift or acclimation to soil texture.

In resource-poor environments, adjustment in plant biomass allocation implies a complex interplay between environmental signals and plant development rather than a delay in plant development alone. To understand how environmental factors influence biomass allocation or the developing phenotype, it is necessary to distinguish the biomass allocations resulting from environmental gradients or ontogenetic drift. Here, we compared the development trajectories of cotton plants (Gossypium herbaceum L.), which were grown in two contrasting soil textures during a 60-d period. Those results distinguished the biomass allocation pattern resulting from ontogenetic drift and the response to soil texture. The soil texture significantly changed the biomass allocation to leaves and roots, but not to stems. Soil texture also significantly changed the development trajectories of leaf and root traits, but did not change the scaling relationship between basal stem diameter and plant height. Results of nested ANOVAs of consecutive plant-size categories in both soil textures showed that soil gradients explained an average of 63.64–70.49% of the variation of biomass allocation to leaves and roots. Ontogenetic drift explained 77.47% of the variation in biomass allocation to stems. The results suggested that the environmental factors governed the biomass allocation to roots and leaves, and ontogenetic drift governed the biomass allocation to stems. The results demonstrated that biomass allocation to metabolically active organs (e.g., roots and leaves) was mainly governed by environmental factors, and that biomass allocation to metabolically non-active organs (e.g., stems) was mainly governed by ontogenetic drift. We concluded that differentiating the causes of development trajectories of plant traits was important to the understanding of plant response to environmental gradients.

Differences and similarities between water sources of Tamarix ramosissima, Nitraria sibirica and Reaumuria soongorica in the southeastern Junggar Basin: Differences and similarities between water sources of Tamarix ramosissima, Nitraria sibirica and Reaumuria soongorica in the southeastern Junggar Basin

Aims Water is the most important limiting factor for plant growth in desert ecosystems. Our objective was to investigate the water sources of three co-existing desert plants and illustrate seasonal variation characteristics in southeastern Junggar Desert in China. Methods We investigated three kinds of desert plants (Tamarix ramosissima, Nitraria sibirica and Reaumuria soongorica) in the same habitat and measured hydrogen and oxygen stable isotope ratio (δD and δ18O) values of their xylem water and potential water sources (precipitation, soil moisture and ground water). The IsoSource model was then used to calculate probable contributions of potential water sources to total plant water uptake. Important findings The water sources of the three desert plants had obvious seasonal characteristics. Reaumuria soongorica and N. tangutorum obtained a high proportion of water from shallow soil water (0–100 cm) in spring. However, during the summer and autumn, R. soongorica tended to use deeper soil water, and N. tangutorum tended to use ground water. Tamarix ramosissima obtained 90% of its water from deep soil water and ground water, and there were no seasonal variations. The three kinds of plants had different water sources closely related to their water use strategies. This shows desert shrubs, through self-regulation, could tend to their optimal phenotypes and maximize water uptake.

What makes Haloxylon persicum grow on sand dunes while H. ammodendron grows on interdune lowlands: a proof from reciprocal transplant experiments

Determining the mechanisms underlying the spatial distribution of plant species is one of the central themes in biogeography and ecology. However, we are still far from gaining a full understanding of the autecological processes needed to unravel species distribution patterns. In the current study, by comparing seedling recruitment, seedling morphological performance and biomass allocation of two Haloxylon species, we try to identify the causes of the dune/interdune distribution pattern of these two species. Our results show the soil on the dune had less nutrients but was less saline than that of the interdune; with prolonged summer drought, soil water availability was lower on the dune than on the interdune. Both species had higher densities of seedlings at every stage of recruitment in their native habitat than the adjacent habitat. The contrasting different adaptation to nutrients, salinity and soil water conditions in the seedling recruitment stage strongly determined the distribution patterns of the two species on the dune/interdune. Haloxylon persicum on the dunes had lower total dry biomass, shoot and root dry biomass, but allocated a higher percentage of its biomass to roots and possessed a higher specific root length and specific root area by phenotypic traits specialization than that of Haloxylon ammodendron on the interdune. All of these allowed H. persicum to be more adapted to water stress and nutrient shortage. The differences in morphology and allocation facilitated the ability of these two species to persist in their own environments.

Profile Changes in the Soil Microbial Community When Desert Becomes Oasis.

The conversion of virgin desert into oasis farmland creates two contrasting types of land-cover. During oasis formation with irrigation and fertilizer application, however, the changes in the soil microbial population, which play critical roles in the ecosystem, remain poorly understood. We applied high-throughput pyrosequencing to investigate bacterial and archaeal communities throughout the profile (0–3 m) in an experimental field, where irrigation and fertilization began in 1990 and cropped with winter wheat since then. To assess the effects of cultivation, the following treatments were compared with the virgin desert: CK (no fertilizer), PK, NK, NP, NPK, NPKR, and NPKM (R: straw residue; M: manure fertilizer). Irrigation had a greater impact on the overall microbial community than fertilizer application. The greatest impact occurred in topsoil (0–0.2 m), e.g., Cyanobacteria (25% total abundance) were most abundant in desert soil, while Actinobacteria (26%) were most abundant in oasis soil. The proportions of extremophilic and photosynthetic groups (e.g., Deinococcus-Thermus and Cyanobacteria) decreased, while the proportions of R-strategy (e.g., Gammaproteobacteria including Xanthomonadales), nitrifying (e.g., Nitrospirae), and anaerobic bacteria (e.g., Anaerolineae) increased throughout the oasis profile. Archaea occurred only in oasis soil. The impact of fertilizer application was mainly reflected in the non-dominant communities or finer taxonomic divisions. Oasis formation led to a dramatic shift in microbial community and enhanced soil enzyme activities. The rapidly increased soil moisture and decreased salt caused by irrigation were responsible for this shift. Furthermore, difference in fertilization and crop growth altered the organic carbon contents in the soil, which resulted in differences of microbial communities within oasis.

Combined effects of snow depth and nitrogen addition on ephemeral growth at the southern edge of the Gurbantunggut Desert, China

Water and nitrogen (N) inputs are considered as the two main limiting factors affecting plant growth. Changes in these inputs are expected to alter the structure and composition of the plant community, thereby influencing biodiversity and ecosystem function. Snowfall is a form of precipitation in winter, and snow melting can recharge soil water and result in a flourish of ephemerals during springtime in the Gurbantunggut Desert, China. A bi-factor experiment was designed and deployed during the snow-covering season from 2009 to 2010. The experiment aimed to explore the effects of different snow-covering depths and N addition levels on ephemerals. Findings indicated that deeper snow cover led to the increases in water content in topsoil as well as density and coverage of ephemeral plants in the same N treatment; by contrast, N addition sharply decreased the density of ephemerals in the same snow treatment. Meanwhile, N addition exhibited a different effect on the growth of ephemeral plants: in the 50% snow treatment, N addition limited the growth of ephemeral plants, showing that the height and the aboveground biomass of the ephemeral plants were lower than in those without N addition; while with the increases in snow depth (100% and 150% snow treatments), N addition benefited the growth of the dominant individual plants. Species richness was not significantly affected by snow in the same N treatment. However, N addition significantly decreased the species richness in the same snow-covering depth. The primary productivity of ephemerals in the N addition increased with the increase of snow depth. These variations indicated that the effect of N on the growth of ephemerals was restricted by water supply. With plenty of water (100% and 150% snow treatments), N addition contributed to the growth of ephemeral plants; while with less water (50% snow treatment), N addition restricted the growth of ephemeral plants.

Comparison of Soil Properties and Microbial Activities between Air-Dried and Rewetted Desert and Oasis Soils in Northwest China

An air-drying and rewetting (AW) experiment was used to examine the responses of soil properties and microbial activities to abrupt alteration of water availability between desert and oasis soils in northwest China. The results revealed that AW increased soil pH and available nitrogen and phosphorus but decreased soil organic matter in the desert, while available phosphorus increased and available nitrogen decreased in the oasis. This AW also caused a burst of microbial activity in both desert and oasis soils, and the magnitude of the AW effect was correlated with the extent of soil rewetting, incubation temperature, land use, and the interaction between rewetting moisture and incubation temperature. The responses of soil properties and microbial activity to AW were greater in the desert than in the oasis. Different soil properties and microorganism composition resulted from land-use change and were likely to be the causes of the different responses to AW in the desert and oasis soils.