Lettuce Growth and Production under Plastic Shading as a Response to different Microclimate Condition: A Preliminary Study of Climate Change Factors Impact on Crops

Crop production is vulnerable to climate variability, especially when it associated with increasing temperature. Results from global and local scale research with different methods consistently showed negative temperature impacts on crop yield especially vegetables. All of studies find that crops are sensitive to changes in temperature (IPCC, 2007; Mendelsohn, 2014). The consistency of these findings suggested that crops are potentially vulnerable to climate change. Environmental extremes that recently magnified by climate change affected several physiological and biochemical process such as photosynthetic activity, metabolism and enzymatic activity (Ayyogari, Sidhya and Pandit, 2014). Even moderate increase of average day or night temperatures could affect the yield and quality of vegetables like spinach, potato, broccoli, and lettuce (Turner and Meyer, 2011). Initially, high temperature reduced leaf area, which reduced radiation intercepted and eventually reduced the biomass. On the other hand, high temperature speeded up phonological development and shortened the period from emergence to flowering and from flowering to maturity; this often turned out to have undesirable traits. Smaller Tomato fruits in size with higher dry matter content and uneven heads with over-sized flower buds in broccoli occurred even at temperatures of only 25oC (Bisbis, Gruda and Blanke, 2019)

Indonesia is a tropical country in the region of Southeast Asia. By the end of the century IPCC scenarios projected that both temperature and precipitations will change; the temperature may rise from 0.72 to 3.92°C while precipitation may decrease by two percent or increase by up to twelve percent (Cruz et al., 2007). Downscaled modeling specific for Indonesia projected that the temperature will rise relatively uniform across all of Indonesia from about 0.1 to 0.3°C per decade for the next 100 years; and other study suggested that the rate of temperature rising for Indonesia will be slightly greater from 0.2 to 0.3°C per decade (Boer and Faqih, 2004).

Indonesia depends much on agriculture productions; both food crops like rice as the staple food and horticulture products are important. While food crops are sensitive to water availability, horticulture products are sensitive to air temperature and humidity. One of the consequences of climate change in a tropical country will be a shift in the areas of cropping; and as crops could invade mountainous area in searching for cooler air it eventually lead to soil erosion and landslides. New crops could be invaded particular area that are currently marginal for cropping because the temperatures were so low, while some previous productive area could become bare soil (Iizumi and Ramankutty, 2015). In long term it will change the land use and endanger the environment. One reason of lacking research in quantifying the impacts of climate change on crops is it needs detailed information on physiological responses of the crops, climate factors effect on crops growth, development, quality and productivity and it is difficult to modify the air temperature (Malhotra, 2017). Moreover, climate change marked by global temperature increase happened on regional and sub-regional scales. For that reason, it is difficult to generalize the impact on vegetable and fruits crop, for growth and development of these crops are influenced by different environmental factors and numerous type with wide diversity makes it even difficult to summarize the potential effects of climate change on growth and yield. For that reason, few studies on the impact of climate change on vegetables have been carried out (Nelson et al., 2010). Therefore, this primary research tried to overcome this problem with planting highland crops on lowland area which has higher temperature area and study what changes experienced in crops growth and production. Lettuce is chosen in this experiment since lettuce is a wild plant native to temperate regions then vulnerable to climate change. Some problems that might happen if the temperatures higher than 30oC are: seedling malformation, low germination potential, decline in plant size, latex accumulation making leaves bitter and rigid, also loss of apical meristem and browned edges. Higher temperatures can also be associated with stem cleft resulting from deficiency of calcium and boron (Mattos et al., 2014). Lettuce seems to be a model crop well studied for light quality and temperature response, since beside temperature lettuce production also depends on light quality and light intensity. In high latitude area, lettuce production may be limited during late spring and summer months because of unfavorable temperatures which exceeding 30/16 °C day/night that increase the risk of bolting (forming of non-desirable flower stalks), tip burn, rib discoloration and leaf bitterness (Ilić et al., 2017). Lettuce was also chosen because as leafy crops, lettuce is representative in examining temperature effects on crop. Leaf area is the main determining factor affecting light interception by crop and lead to biomass production. Therefore, any reduction of leaf expansion rate is usually associated with reduction of photosynthesis and consequent decrease in above-ground biomass, grain yield and quality. We proposed a hypothesis that changing in crops microclimate would affect crop growth and production.