Pine mistletoe is a hemiparasitic shrub that can produce its own photosynthates. There is a lack of knowledge about the interaction of mistletoe and host under varying environmental condition that might influence carbon gain and allocation. In a 13C-pulse labeling experiment with mature Pinus sylvestris (pine) infected by mistletoes grown in naturally dry or irrigated conditions, (1) mistletoe clusters were shielded from 13CO 2 added , and (2) mistletoes or host needles were removed to manipulate the local assimilate and water availability. No 13C signal was found in shielded mistletoes, indicating no carbon transfer from the host to the mistletoe. When the pine needles were removed from girdled branches, no 13C signal was found in the host tissues, implying no carbon transfer from mistletoe to the host. However, mistletoes on needle-removed pine trees accumulated more labelled assimilates and had higher non-structural carbohydrate (NSC) concentrations only under naturally dry conditions but not in irrigated plots. Our results suggest that mistletoes show full carbon autonomy, as they neither receive carbon from nor provide carbon resource to the host trees. Moreover, the high assimilation capacity of mistletoes seems to be constrained by the host water use under dry conditions, suggesting that drought stress is not only negatively impacting trees but also mistletoes. Therefore, we conclude that the hemiparasites live on their own in terms of carbon gain which, however, depends on the water provided by the host tree.

Current increases in not only the intensity and frequency but also the duration of drought events could affect the growth, physiology, and mortality of trees. We experimentally studied the effects of drought duration in combination with fertilization on leaf water potential, gas exchange, growth, tissue levels of non-structural carbohydrates (NSCs), tissue NSC consumption over winter, and recovery after drought release in oak (Quercus petraea) and beech (Fagus sylvatica) saplings. Long drought duration (> 1 month) decreased leaf water potential, photosynthesis, and NSC concentrations in both oak and beech saplings. Nitrogen fertilization did not mitigate the negative drought effects on both species. The photosynthesis and relative height increment recovered in the following rewetting year. Height growth in the rewetting year was significantly positively correlated with both pre- and post-winter root NSC levels. Root carbon reserve is critical for tree growth and survival under long-lasting drought. Our results indicate that beech is more sensitive to drought and fertilization than oak. The present study, in a physiological perspective, experimentally confirmed the view of Ellenberg (2009) that the European beech, compared to oak, may be more strongly affected by future environmental changes.

Nitrogen deposition and land use are known to influence various ecosystems, but how these anthropogenic activities influence community and ecosystem responses to disturbance remains poorly understood. Here we investigated the effects of increased nitrogen deposition and mowing on the resistance and recovery of a temperate semiarid grassland experiencing a three-year drought. Nitrogen addition reduced grassland biomass resistance and increased biomass recovery, whereas annual mowing reduced grassland structural resistance and increased structural recovery. The treatment effects on community biomass resistance and recovery were largely modulated by the stability of the most dominant species, whereas the treatment effects on community structural resistance and recovery were largely modulated by the structural stability of dominant species assemblages. The discrepancy in the response of biomass and structural stability emphasizes the need to study changes across levels of ecological organization for a more complete understanding of ecosystem responses to disturbances under widespread environmental changes.

The Sanjiang Plain is the biggest freshwater wetland locating within northeastern China. Due to climate change and human activities, that wetland has degraded to a successional gradient from the original flooded wetland to dry shrub vegetation and a forest area with lower ground water level, resulting in changes in soil microbiologic structure and functions. The present study investigated the microbial diversity and community structure in relation to soil properties along this gradient. The soil physic-chemical properties changed significantly with degradation. The Shannon variety of soil fungi as well as bacteria varied significantly with successional stage (both P < 0.05). The community structures of soil bacteria and fungi in the early successional stages (i.e., the wetland) were significantly structured via total phosphorus, available nitrogen and total nitrogen concentrations in soils, while those in the later successional stages (i.e., forests) were significantly structured by soil organic carbon, soil pH and available phosphorus concentrations. Our results indicated that variations in the soil environment affected soil microbial communities along a successional gradient from wetland to forests are mainly. These outcomes indicate that above ground plant composition is a forceful determinant of the structure as well as functions of bacterial and fungal communities, might finally causing substantial alterations in ecosystem activity.