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Agroforestry systems are characterized by a high complexity between vegetation components and niche partitioning. In a crop-grass-tree agroforestry system, rape, willow, and grasses were in situ pulse labeled separately with 13CO2 for 6 h, and 13C was traced in shoots, roots, topsoil (0–15 cm) and subsoil (15–30 cm), microbial biomass carbon (C), and dissolved organic C, as well as respiration losses (CO2) up to 28 days after labeling to investigate the effects of vegetation components on C allocation belowground. 13C recovery in roots after 28 days was 7.0% of total assimilated C for grassland, which was 3.5- and 5.2-fold higher than that for rape and willow, respectively. The larger C allocation belowground in grassland was ascribed to its higher root/shoot ratio compared to willow and rape. Grassland facilitated higher accumulation of root-derived C in soil compared to rape (9.2% of recovered 13C) and compared to willow (1.6% of 13C). Willow retained more photosynthetic C aboveground and less was allocated to roots compared to rape. Although the C allocated to the top 15-cm soil was similar between willow and rape, willow facilitated C allocation in deeper soil compared to rape (0.6% vs. 0.2%). This could be explained by the lower microbial activity and subsequent weaker decomposition of rhizodeposits in 15–30-cm depth under willow. The net belowground C inputs in grassland, willow, and rape were 0.53, 0.06, and 0.10 g C m−2 month−1 of vegetation period, including rhizodeposition of 0.24, 0.05, and 0.04 g C m−2 month−1, respectively. Overall, integrating trees and grassland within cropland facilitates higher root-derived C input into soil, thus contributing to the soil C sequestration in agroforestry systems. [ABSTRACT FROM AUTHOR]

Various studies showed a decrease of drought stress specific parameters of plants after silicon (Si) fertilization. But all studies differed in soil Si concentration between the control and Si treatments. As amorphous silica (ASi) was recently found to cause a strong increase of water holding capacity and plant available water in soils, a combined effect of soil moisture and plant response due to Si addition was assumed. In this study, the influence of the soil Si content was excluded by using the same Si enriched soil for treatments of two rice lines, lsi1 mutant defective in Si uptake and its wild‐type rice. Most plant parameters, such as nutrient contents, biomass, specific leaf area, specific root length, leaf water content and C allocation did not differ significantly between the genotypes neither under flooded conditions, nor under drought conditions. Only photosynthesis and stomatal conductance were slightly higher for the wild type in both drought and flooded treatments. Overall, our data showed that Si accumulation within the plant tissues has only a minor effect on plant performance under drought stress. Hence, existing studies should be reinterpreted in light of the fact that Si additions may increase soil water availability. Our data shows that the effect of Si‐fertilization on mitigating drought stress for plants may be less via effects in planta but rather by Si‐fertilization increasing soil water availability to plants. [ABSTRACT FROM AUTHOR]

Background and Aims: Below-ground translocated carbon (C) released as rhizodeposits is an important driver for microbial mobilization of nitrogen (N) for plants. We investigated how a limited substrate supply due to reduced photoassimilation alters the allocation of recently assimilated C in plant and soil pools under legume and non-legume species. Methods: A non-legume ( Lolium perenne) and a legume ( Medicago sativa) were labelled with N before the plants were clipped or shaded, and labelled twice with CO thereafter. Ten days after clipping and shading, the N and C in shoots, roots, soil, dissolved organic nitrogen (DON) and carbon (DOC) and in microbial biomass, as well as the C in soil CO were analyzed. Results: After clipping, about 50 % more C was allocated to regrowing shoots, resulting in a lower translocation to roots compared to the unclipped control. Clipping also reduced the total soil CO efflux under both species and the C recovery of soil CO under L. perenne. The N recovery increased in the shoots of M. sativa after clipping, because storage compounds were remobilized from the roots and/or the N uptake from the soil increased. After shading, the assimilated C was preferentially retained in the shoots of both species. This caused a decreased C recovery in the roots of M. sativa. Similarly, the total soil CO efflux under M. sativa decreased more than 50 % after shading. The N recovery in plant and soil pools showed that shading has no effect on the N uptake and N remobilization for L. perenne, but, the N recovery increased in the shoot of M. sativa. Conclusions: The experiment showed that the dominating effect on C and N allocation after clipping is the need of C and N for shoot regrowth, whereas the dominating effect after shading is the reduced substrate supply for growth and respiration. Only slight differences could be observed between L. perenne and M. sativa in the C and N distribution after clipping or shading. [ABSTRACT FROM AUTHOR]