The wild weather fluctuations wrought by climate change are stressing out our plants. Our resident gardening expert, Professor Geoff Dixon, explains how.
Pests and diseases are familiar causes of plant damage and loss. Less familiar, but becoming more frequent, are stresses resulting from environmental causes.
These are termed abiotic stresses because no living organism is involved. This means there are no visible signs of pests or pathogens. Diagnosis and treatment are, therefore, less straightforward. These causes are a result of interactions between the plant genotype and the prevailing or changing environment.
Damage may only become apparent after harvesting and at the point of consumer use. A typical example of this is internal browning or breakdown of Brussels sprouts. Larger sprouts are more susceptible to stress, with dense leaf packing in the bud, particularly in early and midseason cultivars.
The internal browning of Brussels sprouts is a consequence of plant stress.
A suggested cause is water condensing within the bud, which restricts calcium transport and leads to marginal leaf necrosis (death). This resembles the exudation, or perspiration, of water from leaf edges when growing plants absorb excessive water, flooding the vascular systems following very heavy rainfall and hot weather.
Oedema is another moisture-induced disorder. Symptoms include unattractive wart-like swellings coalescing on leaves and stems, particularly on Brussels sprouts, cabbages, and cauliflowers. These may rupture, becoming corky with a yellowish or brownish appearance.
Moisture-induced damage to cabbage leaves.
These symptoms result from high soil moisture content and high relative humidity associated with hot days and cool nights. Both internal browning and oedema can be minimised by improving soil structure, encouraging rapid drainage by deep cultivation or growing plants on raised beds.
Improving soil structure is becoming an important way to control salt accumulation. Soil structure can be badly damaged by flooding that brings in polluted water. In subsequent vegetable and fruit crops, plant water uptake, nutrient use efficiency, and photosynthesis are all impaired. The effects are seen in poor germination, burnt leaf margin, stunting, and wilting. This damage will be particularly severe with highly organic soils.
Salt accumulation in onion crops. Improving soil structure is one way of addressing this problem.
Abiotic disorders are becoming more common in commercial crops and this is likely to be reflected in gardens and allotments. That is an effect of climatic change, with generally hotter and wetter conditions interspersed by droughts and freezing events.
As a result, plant growth is erratic and exhibits abiotic disorders. Plant breeders, especially in Asia, are actively seeking genetic solutions that will create crops capable of withstanding erratic environments. In parallel,the agro-chemical industry is producing environmentally sustainable compounds and biostimulants to help combat these problems.
>> How else has climate change changed the way our gardens grow, and what can be done to alleviate its effects? Geoff Dixon explored this issue further.
Professor Geoff Dixon is author of Garden practices and their science, published by Routledge 2019.