Impact of biochar application dose on soil microbial communities associated with rubber trees in North East Thailand.

Biochar is a potential tool to mitigate climate change by enhancing C sequestration in soils, but its use as a soil amendment to improve soil fertility and crop yields is still a contentious subject. In North East (NE) Thailand, biochar has been promoted to restore soil fertility in rubber tree plantations. Despite this, there is scarce information on the impact of biochar application on the soil biota, particularly on microbial communities associated with rubber trees. The effects of increasing doses of biochar on microbial communities were investigated in a rubber tree plantation in NE Thailand, 28 months after application. Biochar application resulted in increases of soil pH and nutrient contents and also had an impact on both bacterial and fungal communities. Changes in microbial composition and structure were observed although fungal communities were more markedly affected than bacterial communities. The nature and magnitude of the observed changes were strongly related to soil properties (pH, soil moisture and P content), while biochar dose (5, 10 or 20 tons/ha) effect was not significant. Our results highlight the need for additional research for a better understanding of the impact of biochar application on soil microbial communities and further cascading effects on ecosystem functions.

Diversity of root-associated arbuscular mycorrhizal fungal communities in a rubber tree plantation chronosequence in Northeast Thailand.

Rubber tree (Hevea brasiliensis) is of major economic importance in Southeast Asia and for small land holders in Thailand in particular. Due to the high value of latex, plantations are expanding into unsuitable areas, such as the northeast province of Thailand where soil fertility is very low and therefore appropriate management practices are of primary importance. Arbuscular mycorrhizal fungi (AMF) contribute to plant growth through a range of mechanisms and could play a key role in a more sustainable management of the rubber plantations. We described the diversity of AMF associated with rubber tree roots in Northeast Thailand in relation to tree age and soil parameters along a chronosequence of rubber tree plantations. Cassava fields were included for comparison. Rubber tree and cassava roots harbored high diversity of AMF (111 Virtual Taxa, VT), including 20 novel VT. AMF VT richness per sample was consistently high (per site mean 16 to 21 VT per sample) along the chronosequence and was not related to soil properties. The composition of AMF communities differed between cassava and rubber tree plantations and was influenced by soil texture and nutrient content (sand, K, P, Ca). AMF community composition gradually shifted with the age of the trees. Our results suggest that the high diversity of AMF in this region is potentially significant for maintaining high functionality of AMF communities.