DAILY STEM GROWTH PATTERN IN IRRIGATED APPLE ORCHARDS FROM ARGES COUNTY IN RELATION TO CLIMATE CHANGES

In terms of climate change manifested in the last 30 years in Romania (1982-2011, average data for 29 localities) and characterized by a significant increase in maximum and minimum temperatures, especially in the summer months and increased rainfall deficit, fruit trees farm efficiency is becoming increasingly dependent on strict control of water management through irrigation systems. Thus, the maximum air temperatures experienced average growth trend per decade of 0.88°C, 0.82°C and 0.70°C in June, July and August, respectively, and minimum of 0.61°C, 0.67°C and 0.75°C, in the same months. In this context, ensuring continuous easily accessible soil water content to the root system of the trees, in correlation with plant consumption, has become the most widely used measure to mitigate the negative effects of rising temperatures and rainfall deficits. One of the most accurate methods of water stress early diagnosis and monitoring in a very short step of the fruit trees growth processes is the measurement of trunk diameter variations (SDV) with electronic dendrometers. To highlight the advantages of applying the method to irrigated apple (Malus domestica Borkh.) plantations from the southern Romania, we have organized two experiences with Redix and Braeburn cvs. grafted on M9 in 2009-2012 period. For measurements were used DEX 100 (Dynamax) dendrometers and GP1 dataloggers (Delta-T Devices). It was found that all SDV-derived indices (maximum daily shrinkage (MDS), daily recovery (DR) and daily growth (DG) of the trees trunk between two successive days) may be used for early diagnosis of water and temperature stress. DG was significantly negatively influenced by MDS in both cultivars and in all months of the year, except in September. The Redix cv. DG was inhibited only by the MDS values greater than 0.36 mm. DG is a much less sensitive indicator of water and heat trees stress than MDS. Emergence of water stress was highlighted by two indicators: soil water tension (SMT) and water vapor deficit of the air (VPD). MDS increased with maximum air temperature (MAXT) from 18°C in Redix cv. and only from 25°C in Braeburn cv., which seems to be better adapted to heat stress than Redix cv. We highlighted for Redix cv., using multiple correlation method, the existence of strong interactions between the effects of MAXT and VPD on the one hand and SMT on the other hand, on the reduction of DG. The higher the vapour pressure deficit and maximum temperature, the lower the daily growth due to increased values in the soil moisture tension for Redix cv. in June.