Biochar, plant productivity and community structure: a two-year study in a newly sown legume-rich pasture in Portugal under ambient and reduced precipitation

Biochar, a carbon-rich byproduct of biomass pyrolysis, has increasingly gained attention for its potential to improve soil properties and enhance plant productivity. However, the effects of biochar incorporation in pastures have received little attention. This study presents a large-scale manipulation experiment, investigating the impacts of biochar amendment on plant productivity and community structure in a newly established legume-rich pasture in Portugal, exposed to ambient (100%) and reduced (50%) precipitation, over the course of two growing seasons. Biochar amendment resulted in a boost in productivity, leading to an increase in aboveground biomass in April of ∼50% in both growing seasons. Legume species benefitted more from biochar addition than the other functional groups, at times nearly doubling their biomass. As a result, biochar altered the community structure in both growing seasons. In the first growing season the relative abundance of legumes (i.e. leguminous forbs) significantly increased at the expense of the forbs (i.e. non-leguminous forbs), whilst in the second growing season, it was at the expense of the grasses. Although precipitation manipulation, i.e. reducing the amount of precipitation by 50%, had little to no impact on productivity, community structure and soil parameters, biochar addition did increase soil moisture. However, water availability was not a limiting factor for plant growth, even when vegetation was exposed to reduced precipitation. The addition of biochar led to significantly higher pH and available potassium. These changes were particularly beneficial to the legume species, as higher pH and potassium availability may contribute to enhanced nitrogen fixation. Thus, the productivity boost and changes in community structure were most likely the result of the increase in pH and potassium, and modifications to soil biological and physicochemical properties, enhancing nutrient availability, and ultimately increasing the competitive ability of the legumes. With increasing pressures from intensive land management, and climate change threatening the capacity of Mediterranean pastoral systems to maintain productivity for livestock, biochar amendment can represent a win-win scenario for pastures, contributing towards simultaneously securing productivity and livestock nutrition as well as overall ecosystem health and resilience to global climate change. • Biochar amendment increases aboveground biomass in Mediterranean grasslands. • Biochar amendment changes community structure in legume-rich pastures. • Legume species benefit most from biochar addition in a Mediterranean grassland. • Precipitation reduction has little effect on productivity and community structure.