you must  do the drought stress for each species  separately, but the treatment s must be the same. then it is very easy to compare different species response, providing you have enough replications for each species.

Right Muayed, in order to perform comparative analyses between treatments and species. The same drought stress intensity  should be performed at the same time in all species.

The problem here may become when choosing the species of study. So, I would suggest to know which is the natural distribution of such species and then apply the same reduction of water (same %). 

Which kind of measurements will you perform?

As Muayed mentioned as well, replicates will be very necessary... but it will depends on the variables you measure.

Every species is adpted naturally for drought but if you mean an ecosystem or a part of it the drought may be apllied simultaneously but  if you work of a level of production in agronomic field you use the stress individually.

But I have a little question : Is your work interested wild plants ? were there any experimentation ?

This is for more explaination not other

Good luck

Hi Sarah,

Your experimental design will depend on how you will ultimately analyse and present the data. With any approach you take, always consider what type of statistical analysis you will do with the data. A fantastic reference, that has a wealth of advice on experimental design and statistical analysis, is Quinn and Keough (2002) "Experimental Design and Data Analysis for Biologists". If you haven't already, I highly recommend you go and read/buy this book now.

If you do run the species separately, ensure you control all of the other environmental variables such as solar radiation, relative humidity, temperature, day/night length, as these will all impact on how "droughty" your experiment is. Running your experiment in a controlled growth chamber will work in this case. If you are conducting your experiment in the glasshouse or field then I definitely would recommend running all species simultaneously.

To quantify drought, I would measure plant water potential or if this is not possible then soil water potential. Measuring water potential is a universal parameter, like temperature. If you measured, say, soil water content, then the degree of droughtiness of the soil will depend on soil texture (ie sand v loam v clay soil). Measuring water potential gets around this.

Michael

My conclusion, there is a lot to be learned from comparing species, and not enough scientists have done it. We did something of that kind, with ICARDA scientists and Laval University students, first using in vitro media that have high osmotic pressure, and then, planting many species in the field at a late date which was certain to give heat stress. That trial was done near Aleppo in 2010. The heat stress part is not published, the osmotic stress story is in Cer Res Comm, coauthors Comeau, A., Nodichao, L., Collin, J., Baum, M., Samsatly, J., Hamidou, D., Langevin, F., Laroche, A., et Picard, E. (2010).

Phenology differences are a key problem; however, it is up to the experimenter to devise a meaningful experiment, and that is not easy if both the heat and water deficit are involved.

I was shocked to see that in the field, wild ancestors of wheat flowered when wheat was 100% ripe; as if they had no fear of stress. Wild ancestors spend energy to cover the ground; this modifies soil temperature, thus water taken up is a bit cooler.

I feel there is still a lot to be understood about drought, with new viewpoints. One has to observe nature in greater detail and separate different stresses if possible. Many soil factors become involved when water deficit begins. Some minerals are chromatographed on a very thin layer of water over soil particles; they arrive to the root at different rates from normal - thus nutritional imbalance happens. Fungi that are normally harmless become dangerous (fungi resist very severe osmotic stress). Part of that story is in the publication quoted.

Heat is a killer for many crop species. Climate change will cause serious damage. Good luck, it is a complex matter.

I agree that all individuals of the species in drought study must be placed at the same time. But to determine the amount of stress (e.g. quantity of water, not water, etc.) you must need to consider the species characteristics. Are all from the same habitat?, are all herbs, shrubs or trees or a combination?

It will be prudent to study the growth habits of the various crop species to know their phenological stages before stressing so that the planting is staggered to make sure that the stress is applied at the same time whether at vegetative or flowering stage. I have done this to maize varieties and cowpea varieties in different experiments.

You must treat drought stress separately to each species.  But treatment will be the same to compare.

Selecting for effects like % survival will tests the sensitivity of a variety; under a recurrent condition, like summmer water supply and temperature. Selecting for causal variables involves a modelò a response and different levels of a variable that can vary in legth and intensity.  The real question is how effective are these procedures in coping with  actual variability, a post hoc test that that requires meta analysis as in Camille Parmesan approach.https://www.plymouth.ac.uk/staff/camille-parmesan.

I have found that when working  with severe drought stress, one enters the field of chaotic behaviour. It is impossible to eliminate this, but reducing the chaos component deserves thinking. For example if plants are not in the same pot, they do not suffer the same stress on a hourly basis. Even if they are in the same pot but separated by several cm, there can be chaotic differences in water distribution. Meanwhile my own conclusion is that in nature we must pay much more attention to the temperature and radiative components - this is a flaw with almost all growth cabinet trials. My #1 request about a trial on drought is that it must relate to the real problems on the farm. In Mediterranean areas, barley is grown in drought prone areas. In dry parts of Western Canada, barley does not tolerate drought that well at all, and farmers prefer durum and bread wheat for example. Very few authors have given thought to the reasons; some speculated about it in talks, but written texts on this matter are scarce. And yet, if we cannot explain such major facts, we do not really understand much about drought. Species comparisons in field conditions do matter. Study soil textures, soil temperatures, water distribution profiles. Drought is not a problem in the lab. It is on the farm.