Under a moderate water stress (pod water potential, Ψ№, - 1.5 MPa), induced by stopping irrigation for 3 d, the net photosynthetic rate (PN) decreased to 50 %, transpiration rate (£) to 85 %, stomatal conductance to 65 % and chlorophyll (Chi) content to 82 %, while the activities of photosystems (PS) and of some enzymes of the photosynthetic carbon reduction cycle (NAD- and NADP-glyceraldehyde-3-P dehydrogenases, aldolase) were almost without changes. The exceptions were ribulose-5-P kinase and 3-phosphoglycerate kinase, the activities of which were reduced to 55 and 79 %, respectively. Under a severe water stress (5 d without irrigation, VPW -2.1 MPa) all the above characteristics were strongly reduced (PN to 0.5 %, E to 57 %, PS1 to 62 %, PS2 to 37 %, enzyme activities to 48-68 %), but after rehydration the initial activities were restored. The reduction of PN in pods at a moderate water stress is probably related to the decline in activities of 3-phosphoglycerate kinase and ribulose-5-P kinase, while under a severe stress, when PN is lowered almost to zero, the decline in gs and electron transport activities is very important.
The purpose of this study was to assess how terracing affected overland flow and associated sediment losses, at the micro-plot scale (0.25 m2 ), in recently burnt stands of the two principal forest types in north-central Portugal, i.e. mono-specific stands of Maritime Pine and Eucalypt. Terracing is an increasingly common practice of slope engineering in the study region but its impacts on runoff and erosion are poorly studied. Non-terraced plots at the Eucalypt and the Pine site revealed similar median runoff coefficients (rc: 20-30%) as well as comparable median sediment losses (15-25 g m-2 ) during the first seven months following wildfire. During the ensuing, slightly wetter 18-month period, however, non-terraced plots at the Pine site lost noticeably more sediments (in median, 90 vs. 18 g m-2 ), in spite the runoff response had remained basically the same (median rc: 33 vs. 28%). By contrast, terraced plots at the same Pine site lost hugely more sediments (in median, 1,200 g m-2 ) during this 18-month period. Terraced plots at the Eucalypt site even lost three times more sediments (in median, 3,600 g m-2 ). Ground cover and resistance to shear stress seemed to be key factors in the observed/inferred impacts of terracing.