DOI: 10.5061/dryad.rn8pk0pb6
title: Spatio-temporal dynamics of abiotic and biotic properties explain biodiversity-ecosystem functioning relationships

description: There is increasing evidence that spatial and temporal dynamics of
 biodiversity and ecosystem functions play an essential role in
 biodiversity-ecosystem functioning (BEF) relationships. Despite the known
 importance of soil processes for forest ecosystems, belowground functions
 in response to tree diversity and spatio-temporal dynamics of ecological
 processes and conditions remain poorly described. We propose a novel
 conceptual framework integrating spatio-temporal dynamics in BEF
 relationships and hypothesized a positive tree species richness effect on
 soil ecosystem functions through the spatial and temporal stability of
 biotic and abiotic soil properties based on species complementarity and
 asynchrony. We tested this framework within a long-term tree diversity
 experiment in Central Germany by assessing soil ecosystem functions (soil
 microbial properties and litter decomposition) and abiotic variables (soil
 moisture and surface temperature) for two consecutive years in high
 spatial and temporal resolution. Tree species richness and identity had
 significant effects on soil properties (e.g., soil microbial biomass).
 Structural equation modeling revealed that overall soil microbial biomass
 was partly explained by (a) enhanced temporal stability of soil surface
 temperature and (b) decreased spatial stability of soil microbial biomass.
 Overall, spatial stability of soil microbial properties was positively
 correlated with their temporal stability. These results suggest that
 spatio-temporal dynamics are indeed crucial determinants in BEF
 relationships and highlight the importance of vegetation-induced
 microclimatic conditions for stable provisioning of soil ecosystem
 functions and services.
description: From February 2017 to
 December 2018, five soil samples from each monoculture and five-species
 mixtures were taken every two months to a standard depth of 10 cm using
 cylindrical steel soil corers with a diameter of 2.5 cm. The litter layer
 was removed prior to sampling and restored thereafter. The samples were
 taken in each of the five subplots per plot to account for spatial
 heterogeneity. In 12 campaigns, a total of 1,440 soil samples were taken,
 i.e., 120 samples per campaign. During the sampling, the soil samples were
 cooled and later transferred to a 4°C storing unit for a maximum of 5 days
 until further processing. After the sampling, all samples were sieved at 2
 mm to remove stones, coarse roots, and large animals and to homogenize the
 soil. The soil
 surface temperature was measured for each subplot, utilizing temperature
 loggers (HOBO Pendant® Temperature/Light 8K Data Logger, Onset Computer
 Corporation®, Bourne, USA) placed beneath the litter layer. On plots
 without a thick litter layer (i.e., ash monocultures), the loggers were
 placed on top of the soil without being covered. The temperature was
 logged every 30 min. At the beginning of the
 experiment, one teabag (Lipton® rooibos tea - EAN 87 22700 18843 8, in PVC
 bags) per subplot was placed 5 cm deep into the soil and covered up. Based
 on the assumption that forest soil communities are adapted to complex
 substrates, we used rooibos tea that is known to be relatively
 recalcitrant. Before placing the tea bags in the soil, we oven-dried them
 at 40°C for at least 72 h until no further weight loss was detected to
 remove any water content. After drying and cooling down to constant
 weight, each bag was weighed and labeled with a unique ID to account for
 potential weight deviation caused by the manufacturing process. During
 each soil sampling event, the tea bags were removed and exchanged with a
 new one at the same position. The tea bag IDs and positions were recorded.
 After being taken out of the soil, the exposed bags were again dried in
 the laboratory at 40°C for at least 72 h until no further weight loss was
 detected. After the drying period, each tea bag was opened and their
 content weighed. We calculated the difference between the dried exposed
 tea bag content and its original weight, and subtracted the average (n =
 100) weight of the nylon bag + the string + the plastic label of the bag
 to calculate the mass loss of the tea during the two months of exposure in
 the soil.