Seasonal variation in competitive effect on water stress and pine responses

Abstract

Plant mixtures were established that differed in both proportion and density of loblolly pine (Pinustaeda L.), sweetgum (Liquidambarstyraciflua L.), and broomsedge (Andropogonvirginicus L.). Soil moisture availability to the pine seedlings was quantified every 2 weeks by measuring predawn xylem pressure potentials. Temporal variation in pine water potential was accounted for by a water stress integral approach. Cumulative water stress integral values were calculated over four overlapping periods, from May to June, May to July, May to August, and May to September and compared with the mean seedling stem volume index at each period to determine competitive responses at the whole plant scale. Diurnal measures of stomatal conductance were taken each month to compare competitive responses at the leaf scale. In addition, environmental and plant responses that may control stomatal behavior were quantified. The pine water stress integral was strongly influenced by competing vegetation after the onset of a period of drought in early summer. The correlation between the water stress integral and pine growth increased after a significant drying period, accounting for more than half of the variation in stem volume index at the end of the first growing season. Stomatal conductance was also influenced by competition, with competitive effects more evident during times of drought. Conductance was most often related to bulk leaf water potential, which in turn was related to competitive effects on soil moisture availability. Vapor pressure deficit also influenced stomatal conductance, but this was largely unrelated to competitive effects.

Potential risks for European beech (Fagus sylvatica L.) in a changing climate

“…These findings match with observations made for other drought-sensitive tree species (Woods et al 1990;Fredericksen et al 1991;Perry et al 1994;Backes and Leuschner 2000). The interactive effects of drought and the presence of a fast-growing competing species were less pronounced for the more drought-tolerant Juglans regia (Picon- Cochard et al 2001).…”

Sweetgum: a new look

“…Sweetgum can reduce soil moisture at depths of 60-90 cm in the soil which can directly adversely affect potential growth of the planted P. taeda stand (Mitchell et al 1993). Especially during times of limited water which is common from June to September in much of the pine-sweetgum range, the effect of increased competition by sweetgum can lead to exacerbated water stress and changes in stomatal conductance, the exchange of carbon dioxide molecules through the leaf stomata, which affects photosynthesis (Perry et al 1994).…”

Croissance et fonctions hydriques de plants d épinette noire (Picea mariana (Mill ) B S P ) et de pin gris (Pinus banksiana Lamb ) trois ans après plantation dans des pessières noires à lichens de la forêt boréale commerciale

“…Les pertes en eau sont fonction de la surface foliaire, de la conductance stomatique et du déficit en pression de vapeur de l'air (Burdett 1990). Le potentiel hydrique pré-aube est un bon indicateur du statut hydrique de la plante puisqu'il reflète le potentiel hydrique du sol autour des racines et donne, ainsi, une indication de l'eau disponible dans le sol (Kramer 1983, Schulze 1991, Ellsworth et Reich 1992, Perry et al 1994. Durant les assèchements de sol saisonniers, le potentiel hydrique de la plante (mi-jour et pré-aube) peut changer sur une étendue importante de potentiel hydrique du sol (Schulze 1991 (Hinckley et al 1978, Grossnickle et Heikurinen 1989, Garkoti et al 2003.…”