Tree identity and diversity directly affect soil moisture and temperature but not soil carbon ten years after planting

1. Soil C is the largest C pool in forest ecosystems that contributes to C
sequestration and mitigates climate change. Tree diversity enhances forest
productivity, so diversifying the tree species composition, notably in
managed forests, could increase the quantity of organic matter being
transferred to soils, and alter other soil properties relevant to the C
cycle. 2. A ten-year-old tree diversity experiment was used to study the
effects of tree identity and diversity (functional and taxonomic) on
soils. Surface (0-10 cm) mineral soil was repeatedly measured for soil C
concentration, C:N ratio, pH, moisture and temperature in twenty-four tree
species mixtures and twelve corresponding monocultures (replicated in four
blocks). 3. Soil pH, moisture and temperature responded to tree diversity
and identity. Greater productivity in above- and below-ground tree
components did not increase soil C concentration. Soil pH increased and
soil moisture decreased with functional diversity, more specifically, when
species had different growth strategies and shade tolerances. Functional
identity affected soil moisture and temperature, such that tree
communities with more slow-growing and shade-tolerant species had greater
soil moisture and temperature. Higher temperature was measured in
communities with broadleaf-deciduous species compared to communities with
coniferous-evergreen species. 4. We conclude that long-term soil C cycling
in forest plantations will likely respond to changes in soil pH, moisture
and temperature that is mediated by tree species composition, since tree
species affect these soil properties through their litter quality, water
uptake and physical control of soil microclimates.