Salt, drought, and heat: growing resilience in our perilla

I think everyone has a plant they simply can’t live without. Kkaennip is that plant for me. I anticipate their arrival each season, I set aside time each morning and evening to walk through their fields, and my loved ones know that I will never move outside of the latitudinal range that dictates where they can successfully mature seeds.

My inability to imagine a future without them, my conviction in wanting future generations to know them, has required me to be a keen observer and deliberate partner. I think of what they need, the other plants kkaennip likes to be rotated with or grown adjacent to, the factors that will make them feel welcomed at our farm. In each of the 13 years I’ve grown them, I’ve learned how to tend to them with an increasing sense of attunement. I can notice when they’re stressed, or when they’re at their peak each day. When I see pictures of our seeds growing in other locations, I can tell a little bit about the conditions where they are, based on how they look. This level of familiarity has informed our processes through the years, and has shaped some ongoing curiosities. Beyond working to ensure that our environments are as welcoming as possible, how can we look to the seed’s abilities to evolve with respect to place, and more specifically, to meet the unique stressors presented by those places? How can our attention be refined to amplify the ways the seed is adapting?

Our farm faces a few significant, fundamental pressures. Aside from the intensifying heat and wildfire smoke, our main issues are symphylans and seasonal spikes in groundwater salts. To strategize, we tried to understand if the problem was best confronted through optimizing our management/approach, or through potential selection/heritable resilience on the plant’s part.

Symphylans are small arthropods whose range is typically limited to alluvial soils of the west. They eat the young root hairs of plants, limiting the plant’s ability to build root pressure, and depending on the crop, leads to either death or severe stunting. While different crops are impacted at varying levels of severity, we observe the range of tolerance being mostly based in broad crop categories that vary in how capable they are in surviving their root systems being impaired. We see less heritable gains made in regards to improving tolerance within crop species. Chamoe and aehobak suffer the most when planted in an infested field, and we’ve sadly witnessed over 85% of a planting die within a week. Others, like gochu and perilla, may experience stunting when transplanted into moderately impacted areas, but plants can usually recover, their root systems managing to hold on and grow vigorously when the pressure eases. So management, rather than genetics informs how we strategize. We can focus on timing (planting later in the season once temperatures are >85F when symphylans are driven to deeper, cooler soil levels) and being mindful of crop placement (identifying the range of symphylan populations around the farm, and planting our most susceptible crops in our least impacted fields), to minimize the impact they have on our production.

*Garden symphylan enjoying the good humus life*

Intensifying heat, on the other hand, is something we can see plants respond to and build their tolerance to from season to season. For many of the crops on our farm, perilla included, our farm’s temperatures (which linger at 110-118F for weeks during the summer) are extremely stressful. While the light intensity and warmth mean rapid, vigorous growth, temperatures beyond 104F result in a decline in photosynthetic activity, due to the enzymes within a plant starting to lose shape and functionality.

Extreme heat affects all life on our farm, and while we can’t necessarily set up a controlled experiment with temperature as a variable, we can make continual selections towards individuals within a population that express more resilience. This broad, mass selection means that as long as we can observe some degree of variability in how the overall population deals with a stressor, we can choose which plants we save seeds from. With each successive generation, we can see the bigger population better able to withstand the heat, the idea being that hopefully by saving seeds from the heartiest of plants, whatever interesting things are happening within that plant’s genetic makeup that result in them standing out will be passed on to future plants. Perilla comes from a place in the world where summer is punctuated by monsoon rains and humidity. Dropping them in our arid climate was probably a shock to their system, but after over a decade of astute attention and identifying goals, we have seen a sustained increase in their ability to stay cool, even in the blazing heat.

Population design. Knowing we need at least 75 plants to maintain the long term health and variability of our kkaennip, if we plant 105 plants, we have space to choose from the best 78%. We would essentially choose the best 3 of any 4 plants to save seeds from. If we were to only plant 75, saving seeds from all, we would have a mix of those who performed exceptionally well, and those who perhaps lagged behind. We would have a sort of net gain of zero since we are not choosing to go in any particular direction, and we are not removing plants who display negative traits.

Another pass has us planting 230 plants, allowing us to choose the top 32% to save seeds from. The more room we have to select towards traits that suggest a positive arc in relation to the stressors we face, means potentially faster gains towards long term adaptation. In this plan, we would be able to choose the best 1 of every 3 plants. Being selective about who moves on might seem rude, but it’s in service of increasing their overall odds in an increasingly chaotic future.

Drought tolerance is a trait we can interact with even more meticulously. Since we rely on irrigation for the bulk of our growing season, we can control varying amounts of water for different plots. We can replicate plots within our farm to confirm the role that water or the deprivation of water has on a given population. Different crops have varying ranges of inherent drought tolerance. For some, like different amaranth species, unique anatomic structures (in their case, C4 pathways) confer drought resilience due to limiting photorespiration. Most of the crops we grow on our farm lack these types of natural apparatus to thrive in the absence of water, but they can be pushed in how much water they need. As we mentioned before, perilla enjoys water, and needs a fairly moderate amount to be happy. So to work to improve their survival in dry conditions, we grew sibling plots each season. One control plot represented their baseline in terms of water needs. In the control plot, we gave plants the amount of water that sustained vigorous growth, quality leaf harvests, and successful, even seed maturation. Other plots were our variable plots, where plants received less water (we have also done this for fertilizer/input reduction). The goal was to find the balance of withholding water to an extent where we could see stress expressed in enough of the population, while being able to still save healthy, viable seeds. If we stressed a variable plot too much and saw too great a number of plants succumbing to the pressure, or being unable to make seeds, then we adjusted the volume and frequency of water they received. Over time, our goal was to see if a variable plot could ultimately end up increasing the percentage of plants that thrived with less. When different plots became more consistent with our control plot, we could assume that gradually, plants were adjusting to life with less water, and figuring out how to thrive. If at the beginning of these tests, all plots performed equally well, we could assume that our baseline needed to be adjusted, and that less water was needed than we originally thought. So processes like these help optimize our farm by either developing improvement runways, or letting us know how to refine our practices.

Plot map for different irrigation applications. We adjusted both overall volume of water given, as well as frequency. In plot 2, we could see how plants responded to being given 50% the amount of water as the control plot. In plot 3, we gave plants only an hour less irrigation, but tried to see how well they could endure a longer duration between waterings.

In 2021 a new peril emerged. Our spring seedling production posed unique challenges. Many of our seeds, once they emerged had browning leaf margins, and poor root development. At first I assumed something was wrong with our potting mix, and experimented with different combinations, all to no avail. Some crops grew ok, and I didn’t notice a problem until potting them up or transplanting them when I would notice a poorly formed root system. Perilla was severely impacted, and the symptoms were unfamiliar to me. Part of me sensed that there was an issue with our groundwater, and so I planted (2) sets of (12) 128-cell trays. I used four different potting mixes (3 trays of each, in each set). For one set, I watered them using the groundwater on our farm. The other set, I watered using water that had been treated by Reverse Osmosis (RO), which removes many contaminants, including salts. The results were clear. All 12 trays, across all the four different mediums used, when watered with RO water came up healthy and vigorous. The 12 trays given our untreated groundwater were yellow, brown and malformed, regardless of potting mix.

*Kkaennip emergence with untreated groundwater*

*Seedlings 12 days from emergence with untreated water*

*Root development (or lack thereof) in plants that managed to make it to the field using untreated water. Plugs couldn’t stay together due to lack of root pressure.*

Roots of RO watered seedlings at time of transplant. We should note that these seedlings did get groundwater for a day before going into the field and did experience some browning at their margins subsequently.

That year, we managed to plant 3 rows of plants that had experienced the salt issue as seedlings, and 6 rows that were given RO water. Once in the field, where everyone was receiving the groundwater from our farm, plants initially suffered a little, with us seeing some dieback of older leaves, and challenges in getting established. Mysteriously enough, all rows were able to put on new growth and eventually looked relatively healthy and robust. It seems as though an interaction between potting mixes and our groundwater resulted in particularly bad conditions for our young plant’s growth. I wasn’t certain whether mature plant’s ability to survive was based on their susceptibility decreasing as they moved from their most tender young phase, or if there were enough other mitigating factors in our soil to offset the concentration of salt in the root zone. I moved some seedlings into bigger pots, to see if they too would outgrow the impacts, but they remained stunted. So it drew my attention back to the factors at play in our soil.

There was no conclusive explanation as to why plants fared better in the field than they did in containers. We spent the season trying to better understand different factors like irrigation frequency, the use of mulch and applications of gypsum (the calcium potentially displaces sodium, while also balancing our high magnesium content), as well as noticing which crops were most impacted and how. For instance, nightshades looked ok in terms of leaf development, but their roots were really underdeveloped. Cucurbits managed to do fine, experiencing seemingly no negative impact. Mint family plants like our perilla and basils were the most impacted.

While we may not fully understand what exactly happened that coaxed our perilla crop along through that scarily saline summer, we were relieved that in the fall, plants successfully flowered and set seed. We wondered if those plants were going to pass on anything promising in terms of potential salt tolerance improvement. We saved seeds in batches, some from plants in rows that were given RO water as seedlings, and some from plants given untreated water the whole time.

Fortunately for us, though unfortunately for this experiment, the spike in salts we experienced was not sustained last season. A farm advisor in our area shared that this problem, though not uncommon, is not yet at a point where salinization is moving at a consistent pace. Some years, particularly dry years, might see a rise in different salts and imbalances, while others will level out. In any event, while we continued to see some slightly better color and rapid growth from RO water, we didn’t see any real differences in the seeds saved from the different batches. Seeds from (RO) plants in the previous generation behaved pretty much the same as seeds from untreated water plants. While some research suggests different varieties of perilla may have varying levels of salt tolerance, we don’t have an abundance of germplasm to test this at the moment.

Only time will tell the extent to which selection might help to strengthen salt tolerance in our plants. Our main takeaway is that the practices we employ on the farm interact with each plant’s own abilities to learn and adapt. Whatever challenges await us can be understood and addressed by mindful processes. Plant breeders talk about the role that genetics and environment play (G x E), with different opinions on which factor is more weighted. It’s sort of a botanical version for the nature or nurture debate. Thinking about drought tolerance for example, I think that it’s a clear both/and. Working on our farm, and having structured trials to the best of our ability (given the enormous amount of factors we have no control over), we have made reasonable strides in seeing plants develop more capacity to grow with less water. But simultaneous to the plant’s journey, is the changing quality of our soil, and as we build organic matter, our soil’s capacity to retain water and efficiently recharge groundwater during the rainy season, means each successive wave of plants is met by an improved environment in which to grow. Genetics and environment can work in concert with one another yielding a result that exceeds the sum of its parts. Perilla is on a 3 or 5 year rotation cycle, and at our current farm site, where we’re entering our 6th season, we have just begun to see plants return to fields where they have grown before. It’s a sweet way of marking time passing, recognizing the fundamental nature of change, and appreciating the ways in which loving one being can lead us into an ever complex web of accountability and care.