<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Hussain, M Z</style></author><author><style face="normal" font="default" size="100%">Otieno, D O</style></author><author><style face="normal" font="default" size="100%">Mirzae, H</style></author><author><style face="normal" font="default" size="100%">Li, Y L</style></author><author><style face="normal" font="default" size="100%">Schmidt, M W T</style></author><author><style face="normal" font="default" size="100%">Siebke, L</style></author><author><style face="normal" font="default" size="100%">Foken, T</style></author><author><style face="normal" font="default" size="100%">Ribeiro, N.a.</style></author><author><style face="normal" font="default" size="100%">Pereira, J S</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">CO2 exchange and biomass development of the herbaceous vegetation in the Portuguese montado ecosystem during spring</style></title><secondary-title><style face="normal" font="default" size="100%">Agriculture, Ecosystems &amp; Environment</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Ecosystem productivity</style></keyword><keyword><style  face="normal" font="default" size="100%">Environmental regulators</style></keyword><keyword><style  face="normal" font="default" size="100%">Herbaceous layer</style></keyword><keyword><style  face="normal" font="default" size="100%">montado</style></keyword><keyword><style  face="normal" font="default" size="100%">Net ecosystem CO2 exchange</style></keyword><keyword><style  face="normal" font="default" size="100%">Soil moisture</style></keyword><keyword><style  face="normal" font="default" size="100%">Spring period</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2009</style></year></dates><volume><style face="normal" font="default" size="100%">132</style></volume><pages><style face="normal" font="default" size="100%">143-152</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Montado are spatially heterogeneous ecosystems that are economically important for the production of cork and herbaceous biomass that provide fodder for animals. Understanding of how trees and the herbaceous layer interact to determine pasture yield and the overall CO2 exchange of the herbaceous layer is crucial. Portable chambers were used to study CO2 exchange by the herbaceous layer component of the montado ecosystem in southern Portugal. Biomass, Net herbaceous layer CO2 exchange (NEE) and respiration (Reco) were measured in the open and understory locations between March and May, during the active growing period. Parameter ﬁts on the NEE data were performed using empirical hyperbolic light response model, while ecosystem respiration (Reco) data were ﬁtted with a two-parameter exponential model. Annual green biomass productions were 405.8 9.0 and 250.6 6.3 g m2 in the open and the understory, respectively. The respective maximum NEE during the day were 24.0 2.9 and 9.6 2.2 mmol m2 s 1 while maximum Reco were 20.6 2.2 and 10.0 1.6 mmol m2 s 1 , occurring in April. Photosynthetic photon ﬂux density (PPFD) explained more that 70% of variations in daytime NEE while soil temperature at 10 cm depth (Tsoil ) explained &gt;50% of the variations in Reco under non-limiting soil moisture conditions. Both the herbaceous layer communities shared similar plant functional types and no signiﬁcant difference in nutrient nitrogen (N) occurred between them. The two herbaceous layer components shared similar physiological characteristics and differences that arose in their CO2 uptake capacities and green biomass production were the result of microclimatic differences created by tree shading</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Otieno, D O</style></author><author><style face="normal" font="default" size="100%">Kurz-Besson, C</style></author><author><style face="normal" font="default" size="100%">Liu, J</style></author><author><style face="normal" font="default" size="100%">Schmidt, M W T</style></author><author><style face="normal" font="default" size="100%">Do, R Vale-Lobo</style></author><author><style face="normal" font="default" size="100%">David, T S</style></author><author><style face="normal" font="default" size="100%">Siegwolf, R</style></author><author><style face="normal" font="default" size="100%">Pereira, J S</style></author><author><style face="normal" font="default" size="100%">Tenhunen, J D</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Seasonal Variations in Soil and Plant Water Status in a Quercus suber L. Stand: Roots as Determinants of Tree Productivity and Survival in the Mediterranean-type Ecosystem</style></title><secondary-title><style face="normal" font="default" size="100%">Plant and Soil</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Drought stress</style></keyword><keyword><style  face="normal" font="default" size="100%">leaf water potential</style></keyword><keyword><style  face="normal" font="default" size="100%">osmotic adjustment</style></keyword><keyword><style  face="normal" font="default" size="100%">oxygen isotope</style></keyword><keyword><style  face="normal" font="default" size="100%">root distribution</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2006</style></year></dates><volume><style face="normal" font="default" size="100%">283</style></volume><pages><style face="normal" font="default" size="100%">119-135</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Studies were conducted to examine changes in soil (Ys) and plant water status during summer in a 16-year old Quercus suber plantation in southern Portugal. Continuous measurements were conducted between May 2003 and August 2004, while discontinuous measurements were conducted on a monthly basis between May and September 2003 and repeated between March and September 2004. Intensive measurements were conducted on ﬁve trees with mean height and DBH of 5.3 m and 11.6 cm, respectively, growing at close proximity to each other. Weather conditions and soil water potential (Ys) at the rhizosphere of each of the trees measured at 0.3 and 1 m soil depth were continuously monitored. Predawn (Ypd) and midday (Ymd) leaf water potentials were determined every month. Soil and plant samples were also collected in June and September from diﬀerent locations within the study site for d 18 O isotope composition analysis. Pressure–volume (p–v) curves were constructed from plant shoots at diﬀerent times during the vegetative period to determine osmotic potential at full saturation (P 100 ), water potential at turgor loss point (Ytlp), relative water content at turgor loss point (R*tlp) and bulk modulus of elasticity (e). Signiﬁcant P &lt; 0.05 decline in Ys occurred between May and September, the lowest value recorded being –2.0 MPa. Decline in soil moisture aﬀected tree water status, but decline in leaf water potential varied signiﬁcantly (P &lt; 0.05) among the trees. At the end of summer drought, lowest Ypd measured was –1.7 MPa while the highest measured during this time was –0.8 MPa. Diﬀerences among trees were attributed to diﬀerences in rooting depth, as shown by regression analysis of 18 O isotopes. Radial stem growth ceased when Ys within the upper 0.3 m depth approached –1.5 MPa. The upper soil layers contributed approximately 33% of the total tree water requirement, between spring and mid summer when drought was experienced by trees. Deep soil layers however, supplied most of the water required during drought and no growth was recorded during this time. Stressed trees increased solute concentration of their tissues by a Magnitude of 0.7 MPa while bulk tissue elastic modulus increased by about 17 MPa. The study emphasizes the signiﬁcance of roots as determinants of tree productivity and survival in the Mediterranean ecosystems.</style></abstract></record></records></xml>