Biomass and water partitioning in two age-related Caragana korshinskii plantations in desert steppe,northern China

Understanding of biomass and water allocation in plant populations will provide useful information on their growth pattern and resource allocation dynamics. By direct measurement, the biomass and water content partitioning were compared at the aboveground, belowground and whole-plant levels for artificial Caragana korshinskii populations between 6- and 25-year-old sites in desert steppe, northern China. The biomass was mainly allocated to third-srade branches at the aboveground level, and to firstand second-grade roots at the belowground level, and to aboveground parts at the whole-plant vegetative level. Those plant parts mentioned above became the major component of biomass pool of these shrub populations. Biomass pattern changed significantly at aboveground and/or whole-plant levels （P 〈0.05）, but not at belowground level （P 〉0.05） at 25-year-old site in comparison to 6-year-old site. Also, the water relations between dif- ferent plant parts changed considerably at all three levels from 6- to 25-year-old sites. These results imply that biomass pattern and relative water content of plant parts are correlated with the process of plantation development. The ratio of belowground to aboveground, though below 1, increased from 6- to 25-year-old site. These results suggest that these shrub populations can adjust biomass partition and relative water content of different compartments to alter their ecological adaptive strategies during stand development in desertified regions.

The Impact of Animal Trampling on Free-living Nematode Abundance,Genera,and Trophic Diversity was Attenuated by Tree Canopies

Livestock grazing and trampling is an important factor in the formation and development of different terrestrial ecosystems.However,despite numerous studies on soil compaction,there is still no consensus as to which kind of effect(positive or negative)animal trampling exerts on soil nematodes.The main goal of this study was to evaluate the animal trampling effect on free-living nematode abundance and diversity,and to define the attenuating effect of the tree canopies(Cupressus sempervirens,Eucalyptus camaldulensis,and Tamarix aphylla)during wet and dry periods.The nematodes were extracted from 100 g aliquots of soil samples(brown-red sandy soils)during cold-wet(CW),warm-wet(WW),and hot-dry(HD)periods during 2013-2014,in a man-made safari-zoo habitat,using the Baermann funnel procedure.Our results revealed the impact of trampling on both free-living nematode abundance and diversity,and their soil habitat.It was found that trampling,along with seasonal fluctuation and the tree-species attenuating effect on the soil medium,resulted in the creation of the spatial-temporal heterogeneity of soil properties in the study area.In turn,variation in soil properties was reflected in soil nematode abundance and diversity,revealing tight correlation with the observed soil properties.Animal trampling had an overwhelming,mostly negative impact on soil nematode abundance,genera,and trophic diversity in the open,bare area.However,the protective effect of the tree canopies,as well as seasonal fluctuations,attenuated this negative impact.The trees had a significant attenuating effect on trampling compared with the open,bare area.However,different tree species during the wet and dry periods had a variable impact on nematode abundance,genera,and trophic diversity.During the hottest period of the year,when external adverse factors dominated the trampling effect,the ability of the trees to protect nematode communities was significantly reduced.Of all the colonizer-persister(cp)continuum of nematode functional guilds,only bacteria-feeding nematodes belonging to the cp-1 guild were positively affected by trampling.In general,nematodes belonging to the r-life-strategy group(colonizers tolerant to environmental disturbance),mainly bacteria-feeding nematodes,were the most numerous(61 and 44%at the trampling and undisturbed sites,respectively).In contrast to the bacteria-feeding group,fungi-feeding nematodes were the smallest group in the study area(8 and 4%in the trampling and undisturbed sites,respectively).The undisturbed sites were a more favorable habitat for the plant-parasite nematodes(9 and 26%in the trampling and undisturbed sites,respectively).Surprisingly,the omnivore-predator nematodes belonging to the K-life strategy group and that are characterized by hypersensitivity to disturbance,were relatively numerous at the trampling(22%)and relatively undisturbed(26%)sites.The results showed that 62%of the nematode species were affected(48%negatively and 14%positively)by either direct trampling or changes in soil properties.The ecological indices confirmed that animal trampling had a negative impact on the soil biota in the study area.Our results suggested that animal trampling exerts significant a direct and indirect effects(through changes in soil properties)on soil free-living nematodes.Moreover,the wet-dry seasonal periods along with the tree canopies protective effect may significantly change the extent of animal trampling impact.