Root dynamics and interactions in a nutrient-poor and drying species-rich woodland

TESTE, F.P.; KINGSLEY W. DIXON; ERIK J. VENEKLAAS; MARCHESINI, V.A.; LAMBERS, H.

Congreso; VI Reunión Binacional de Ecología -XXVII Reunión Argentina de Ecología ? XXIII Reunión de la Sociedad Chilena de Ecología; 2016

Climate change is decreasing the amount and delaying thestart of winter rains in southern hemisphere Mediterraneanecosystems. Important components of western Australia?sMediterranean biodiversity hotspot are the Proteaceaesuch as Banksia species. These plants rely on threshold-soilmoisture levels to deploy their efficient nutrient-mobilisingcluster roots to gather poorly-available nutrients fromextremely phosphorus (P)-impoverished soils. The physiologyof cluster-rooted plants has been well studied howevertheir responses under climate change are largely unknown.We determined the root dynamics with minirhizotronmeasurements in a eucalypt-banksia woodland with orwithout irrigation to mimic the current reduced rainfall (basedon long-term averages). Furthermore, we estimated thelifespan of the different root types, root intermingling, andcluster root P remobilisation. Irrigation produced a noticeableyet small increase in root production only in june. Standingcrop was generally greater in non-irrigated plots and rootmortality was independent of irrigation. Survival analysesof the different root types encountered with the clusterroots revealed considerable effects of soil depth on lifespan.Despite predictions from plant ecophysiological studies onthe aboveground responses to a drying climate, we onlyfound small transient effects on root production. However,there was a considerable effect of irrigation on the frequencyof root intermingling and we suggest that root interactionsmay become less prominent under a drying climate. Root Premobilisation in cluster roots was efficient, only leaving ~10 % of P behind suggesting that if any form of nutrient-uptakefacilitation takes place during root intermingling, it likelyinvolves a form of kleptoparisitism. We propose that rootsin this system and presumably other ecosystems show someresilience to a modified precipitation regime but this was notthe case for interspecific root interactions. We suggest that ifnutrient-uptake facilitative interactions decline under a dryingclimate so will root-driven mechanisms that promote plantspecies coexistence and the maintenance of diversity.