Species Richness Interacts with Drought to Affect Litter Decomposition via its Effect on Litter Nitrogen Concentration

Biodiversity loss, exotic plant invasions and climatic change are currently the three major challenges to our globe and can each affect various ecological processes, including litter composition. To gain a better understanding of global change impacts on ecological processes, these three global change components need to be considered simultaneously. Here we assembled experimental plant communities with species richness levels (1, 2, 4, 8 or 16) and subjected them to drought (no, moderate or intensive drought) and invasion (invasion by the exotic annual plant Symphyotrichum subulatum or not). We collected litter of the native plant communities and let it decompose for nine months within the communities. Drought decreased litter decomposition, while the exotic plant invasion had no impact. Increasing species richness decreased litter decomposition under the mesic condition (no drought), but had little impact under moderate and intensive drought. A structural equation model showed that drought and species richness affected litter decomposition mainly via influencing litter nitrogen concentration, but not via altering the quantity and diversity of soil meso-fauna or soil physio-chemical properties. The negative impact of species diversity on litter decomposition under the mesic condition was mainly ascribed to a sampling effect, i.e. via particularly low litter nitrogen concentrations in the two dominant species. Our results indicate that species richness can interact with drought to affect litter decomposition via effect on litter nitrogen. We conclude that nitrogen-dependent litter decomposition should be a mechanism to predict integrated effects of plant diversity loss, exotic plant invasions and climatic change on litter decomposition.

Decomposition of Herbivore-Damaged Leaves of Understory Species Growing in Oak and Pine Stands

Leaves are the largest component of forest litter. Their decomposition rate depends mainly on plant species, leaf chemical composition, microorganism biodiversity, and habitat conditions. It is known that herbivory by insects can modify the chemical composition of leaves, such as through induction. The aim of this study was to determine whether the rate of leaf decomposition is related to the susceptibility of the plant species to insect feeding and how leaf damage affects this rate. For our research, we chose six species differing in leaf resistance to insect damage: Cornus sanguinea, Frangula alnus, and Sambucus nigra (herbivore resistant), and Corylus avellana, P. padus, and Prunus serotina (herbivore susceptible). The decomposition of these plant leaves was examined in two monoculture forest stands, deciduous (Quercus robur) and coniferous (Pinus sylvestris). Litter decay rate k and change of litter mass, content of defensive metabolites (total phenols (TPh) and condensed tannins), and substances beneficial for organisms decomposing litter (nitrogen (N) and nonstructural carbohydrates (TNC)) were determined. Contrary to our expectations, leaf litter of herbivore-resistant species decomposed faster than that of herbivore-susceptible species, and damaged leaves decayed faster than undamaged leaves. We found that faster decaying leaf litter had a lower content of defensive compounds and a higher content of TNC and N, regardless of the plant species or leaf damage. Leaf litter decomposition caused a large and rapid decrease in the content of defensive compounds and TNC, and an increase in N. In all species, the tannin content was lower in damaged than in undamaged leaves. This pattern was also observed for TPh, except in S. nigra. We interpret this as the main reason for faster decay of damaged leaves. Moreover, the loss of leaf mass was greater under oak than pine stands, indicating that the microorganisms in deciduous stands are more effective at decomposing litter, regardless of leaf damage.

Microbial inputs at the litter layer translate climate into altered organic matter properties

<p>Plant litter chemistry is altered during decomposition but it remains unknown if these alterations, and thus the composition of residual litter, will change in response to climate. Selective microbial mineralization of litter components and the accumulation of microbial necromass can drive litter compositional change, but the extent to which these mechanisms respond to climate remains poorly understood. We addressed this knowledge gap by studying needle litter decomposition along a boreal forest climate transect. Specifically, we investigated how the composition and/or metabolism of the decomposer community varies with climate, and if that variation is associated with distinct modifications of litter chemistry during decomposition. We analyzed the composition of microbial phospholipid fatty acids (PLFAs) in the litter layer and measured natural abundance δ<sup>13</sup>C<sub>PLFA</sub> values as an integrated measure of microbial metabolisms. Changes in litter chemistry and δ<sup>13</sup>C values were measured in litterbag experiments conducted at each transect site. A warmer climate was associated with higher litter nitrogen concentrations as well as altered microbial community structure (lower fungi:bacteria ratios) and microbial metabolism (higher δ<sup>13</sup>C<sub>PLFA</sub>). Litter in warmer transect regions accumulated less aliphatic‐C (lipids, waxes) and retained more O‐alkyl‐C (carbohydrates), consistent with enhanced <sup>13</sup>C‐enrichment in residual litter, than in colder regions. These results suggest that chemical changes during litter decomposition will change with climate, driven primarily by indirect climate effects (e.g., greater nitrogen availability and decreased fungi:bacteria ratios) rather than direct temperature effects. A positive correlation between microbial biomass δ<sup>13</sup>C values and <sup>13</sup>C‐enrichment during decomposition suggests that change in litter chemistry is driven more by distinct microbial necromass inputs than differences in the selective removal of litter components. Our study highlights the role that microbial inputs during early litter decomposition can play in shaping surface litter contribution to soil organic matter as it responds to climate warming effects such as greater nitrogen availability.</p>

Effects of decomposed poultry litter, nitrogen and phosphorus on growth and micronutrient content of arum (Colocasia esculentus L.)

A pot experiment was carried out to evaluate the integrated effects of poultry litter, nitrogen and phosphorus on the growth and micronutrient (Fe, Zn and Cu) contents of arum (Colocasia esculenta L.) in the net house of the Department of Soil, Water and Environment, University of Dhaka. Height (76 cm), leaf number (5 no./plant), leaf area (1045.66 cm2/plant) and fresh (130.7 g/plant) and dry (14.35 g/plant) weights of leaf, stem, bulb and root were achieved highest in the combined application of decomposed poultry litter compost and nitrogen (PL2N40P0). The leaf area, and fresh and dry weights of leaf, stem, bulb and root varied significantly (p≤ 0.5). The concentration of iron, zinc and copper in different parts were measured the highest in the treatments (0.70%), (0.58%), (0.22%) for leaf; (0.83%), (0.96%), (0.99%) for stem; (0.74%), (0.09%), (0.05%) for bulb and (0.98%), (0.64%), (0.27%) for root, respectively. Generally, the concentrations of Fe, Zn and Cu were found to be the highest in PL4N20P15, PL4N0P15 and PL2N0P0 treatments, respectively.J. Biodivers. Conserv. Bioresour. Manag. 2018, 4(1): 11-18

Microbial respiration per unit microbial biomass depends on soil litter carbon-to-nitrogen ratio

Soil microbial respiration is a central process in the terrestrial carbon (C) cycle. In this study I tested the effect of the carbon-to-nitrogen (C : N) ratio of soil litter layers on microbial respiration in absolute terms and per unit microbial biomass C. For this purpose, a global dataset on microbial respiration per unit microbial biomass C – termed the metabolic quotient (qCO2) – was compiled form literature data. It was found that the qCO2 in the soil litter layers was positively correlated with the litter C : N ratio and negatively related with the litter nitrogen (N) concentration. The positive relation between qCO2 and litter C : N ratio resulted from an increase in respiration with the C : N ratio in combination with no significant effect of the litter C : N ratio on the soil microbial biomass C concentration. The results suggest that soil microorganisms respire more C both in absolute terms and per unit microbial biomass C when decomposing N-poor substrate. Thus, the findings indicate that atmospheric N deposition, leading to decreased litter C : N ratios, might decrease microbial respiration in soils.