Root endophytic fungal communities associated with pitch pine, switchgrass, and rosette grass in the pine barrens ecosystem

Almost all plants in nature harbour fungi in their roots but the knowledge on distribution and the underlying principles of assemblage is still poorly developed for the root-associated fungi. In this study we analysed the root endophytic fungal communities associated with switchgrass, rosette grass, and pitch pine in the acidic, oligotrophic pine barrens ecosystem. A total of 434 fungal isolates were obtained from 600 root segments of 60 plant samples. DNA barcoding and morphological analyses identified 92 fungal species, which belong to 39 genera in six classes. Compared to other ecosystems, the pine barrens has a higher proportion of Leotiomycetes. The fungal community associated with pitch pine was significantly different from those associated with the grasses, while less difference was found between those associated with the two grasses. Our results suggest that edaphic factors and host specificity play a role in shaping root endophytic fungal community. This study also corroborates our previous finding that plant roots in the pine barrens are a rich reservoir of novel fungi.

Canopy stomatal conductance following drought, disturbance, and death in an upland oak/pine forest of the new jersey pine barrens, USA

Stomatal conductance controls carbon and water fluxes in forest ecosystems. Therefore, its accurate characterization in land-surface flux models is necessary. Sap-flux scaled canopy conductance was used to evaluate the effect of drought, disturbance, and mortality of three oak species (Quercus prinus, Q. velutina, and Q. coccinea) in an upland oak/pine stand in the New Jersey Pine Barrens from 2005 to 2008. Canopy conductance (G(C)) was analyzed by performing boundary line analysis and selecting for the highest value under a given light condition. Regressing G(C) with the driving force vapor pressure deficit (VPD) resulted in reference canopy conductance at 1 kPa VPD (G(Cref)). Predictably, drought in 2006 caused G(Cref) to decline. Q. prinusG(Cref) was least affected, followed by Q. coccinea, with Q. velutina having the highest reductions in G(Cref). A defoliation event in 2007 caused G(Cref) to increase due to reduced leaf area and a possible increase in water availability. In Q. prinus, G(Cref) quadrupled, while doubling in Q. velutina, and increasing by 50% in Q. coccinea. Tree mortality in 2008 led to higher G(Cref) in the remaining Q. prinus but not in Q. velutina or Q. coccinea. Comparing light response curves of canopy conductance (G(Cref)) and stomatal conductance (g(S)) derived from gas-exchange measurements showed marked differences in behavior. Canopy G(Cref) failed to saturate under ambient light conditions whereas leaf-level g(S) saturated at 1,200 μmol m(-2) s(-1). The results presented here emphasize the differential responses of leaf and canopy-level conductance to saturating light conditions and the effects of various disturbances (drought, defoliation, and mortality) on the carbon and water balance of an oak-dominated forest.